### Install Pancake PHP SDK

Source: https://github.com/pancakeapp/php-sdk/blob/master/README.md

Use Composer to install the Pancake PHP SDK. This is the primary method for adding the SDK to your PHP project.

```bash
composer require pancake/sdk
```

--------------------------------

### Initialize Pancake Server Connection

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Instantiate the Server class with your Pancake installation URL and API key. The constructor automatically formats the URL for the API endpoint. This object is required for all subsequent SDK operations.

```php
<?php
use \Pancake\Server;
use \Pancake\ApiException;

require 'vendor/autoload.php';

// Provide your Pancake installation URL and API key.
// The constructor normalizes the URL to .../index.php/api/1/ automatically.
$server = new Server(
    "https://billing.example.com/pancake",
    "vvRVmZQvysA1ndKpmZgJoQNwW0wb8nVzwZ4axTvz"
);

// server->get() and server->post() are available for raw API calls.
// All higher-level classes accept $server as their first argument.

```

--------------------------------

### Server - Initialize Connection

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

The Server class is the entry point for SDK operations. It initializes a GuzzleHttp client configured for the Pancake API base URL and automatically injects the API key into every request.

```APIDOC
## Server — Initialize Connection

`Server` is the entry point for every SDK operation. It wraps a GuzzleHttp client configured for the Pancake API base URL and injects the API key into every request automatically.

```php
<?php
use \Pancake\Server;
use \Pancake\ApiException;

require 'vendor/autoload.php';

// Provide your Pancake installation URL and API key.
// The constructor normalizes the URL to .../index.php/api/1/ automatically.
$server = new Server(
    "https://billing.example.com/pancake",
    "vvRVmZQvysA1ndKpmZgJoQNwW0wb8nVzwZ4axTvz"
);

// server->get() and server->post() are available for raw API calls.
// All higher-level classes accept $server as their first argument.
```
```

--------------------------------

### Create New Invoice with Line Items and Files

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Instantiate an Invoice, configure its properties and line items, then call save() to POST it to the API. On success, the object is reloaded with the server-assigned unique_id and all computed fields. Supports adding standard, flat-rate, and discount line items, as well as attaching files.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoice;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = new Invoice($server);
    $invoice->client_id   = 2;
    $invoice->description = "Web Development Services — Q2 2024";
    $invoice->notes       = "Net 30 payment terms apply.";
    $invoice->type        = "DETAILED"; // Default; also supports "LOGGED_TIME"

    // Line items — taxes can be a name, a percentage string, or a tax ID.
    $invoice->addStandardLineItem(
        "Website Redesign",  // name
        1,                   // qty
        3500.00,             // rate
        ["VAT", "10%"],      // taxes (name or percentage; created if missing)
        "Full redesign",     // description
        0                    // discount
    );
    $invoice->addFlatRateLineItem("Hosting Setup", 150.00, [], "Annual hosting fee", 0);
    $invoice->addFixedDiscountLineItem("Loyalty Discount", 100);       // $100 off
    $invoice->addPercentageDiscountLineItem("Referral Discount", 5);   // 5% off

    // Attach files (URL or local path)
    $invoice->addFile("https://example.com/assets/contract.pdf");
    $invoice->addFile("/tmp/scope-of-work.pdf");
    $invoice->addFileFromContents("Payment due within 30 days.", "terms.txt");

    $result = $invoice->save();
    // $result['unique_id'] is now populated
    echo "Created invoice: {$invoice->unique_id}\n";
    echo "Total: {$invoice->currency_symbol}{$invoice->total}\n";

} catch (ApiException $e) {
    echo "API Error: " . $e->getMessage();
    var_dump($e->getResponse());
}

```

--------------------------------

### Set Up Partial Payment Schedule for Invoice

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Use addPaymentPart() to define a payment schedule before saving a new invoice. This method allows specifying whether the amount is a percentage or a fixed value, the amount, the due date, and notes for each payment part.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoice;
use \Carbon\Carbon;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = new Invoice($server);
    $invoice->client_id = 3;

    $invoice->addStandardLineItem("Consulting", 10, 200.00, [], "10 hours @ $200", 0);

    // 50% due immediately
    $invoice->addPaymentPart(
        true,              // is_percentage
        50,                // amount (50%)
        Carbon::now(),     // due date (Carbon instance)
        "Deposit due now"  // notes
    );

    // Remaining 50% due in 30 days
    $invoice->addPaymentPart(
        true,
        50,
        Carbon::now()->addDays(30),
        "Balance due on project completion"
    );

    $result = $invoice->save();
    echo "Invoice {$result['unique_id']} created with 2-part payment schedule.\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}

```

--------------------------------

### Fetch Reusable Invoice Items

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Retrieves all pre-defined reusable line items from Pancake. Useful for populating item pickers or auto-filling invoices. Also shows how to fetch a specific item by its ID.

```php
<?php
use \Pancake\Server;
use \Pancake\ReusableInvoiceItems;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    // Fetch all reusable items
    $items = ReusableInvoiceItems::get($server);
    foreach ($items as $item) {
        echo "{$item['id']}: {$item['name']} — \\\${$item['rate']}\n";
    }

    // Fetch a specific item by ID
    $item = ReusableInvoiceItems::getById($server, 3);
    echo "Item #{$item['id']}: {$item['name']}, rate={$item['rate']}, description={$item['description']}\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}

```

--------------------------------

### Fetch All Invoices

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Use Invoices::get() to retrieve all invoices from the server. This method returns an array of hydrated Invoice objects. Ensure proper error handling with a try-catch block for ApiException.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoices = Invoices::get($server);

    foreach ($invoices as $invoice) {
        // Read-only computed fields are available directly as properties.
        echo sprintf(
            "Invoice %s | Client %d | Status: %s | Total: %s%.2f | Paid: %s\n",
            $invoice->invoice_number,
            $invoice->client_id,
            $invoice->status,
            $invoice->currency_symbol,
            $invoice->total,
            $invoice->is_paid ? 'Yes' : 'No'
        );
    }
    // Output:
    // Invoice INV-001 | Client 4 | Status: sent | Total: $250.00 | Paid: No
    // Invoice INV-002 | Client 7 | Status: paid | Total: $1200.00 | Paid: Yes

} catch (ApiException $e) {
    $response = $e->getResponse();
    var_dump($response); // Array with Pancake error details or raw HTML on server error
}

```

--------------------------------

### Record Payment Against an Invoice

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Use addPayment() to post a payment record against an existing invoice. This automatically reloads the invoice to reflect the updated paid_amount and status. It supports specifying amount, gateway, datetime, status, transaction ID, fee, and whether to send a notification email.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");

    $success = $invoice->addPayment(
        500.00,             // amount
        "Stripe",           // gateway name
        time(),             // payment datetime (Unix timestamp; null = now)
        "Completed",        // payment status
        "ch_3OxABC123",     // transaction ID
        14.50,              // transaction fee
        true                // send notification email to client
    );

    if ($success) {
        echo "Payment recorded.\n";
        echo "Paid so far:  {$invoice->currency_symbol}{$invoice->paid_amount}\n";
        echo "Still owed:   {$invoice->currency_symbol}{$invoice->unpaid_amount}\n";
        echo "Status:       {$invoice->status}\n";
    }

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}

```

--------------------------------

### ApiException

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Handles errors thrown by SDK operations on API or network failures.

```APIDOC
## ApiException — Error Handling

`ApiException` is thrown by all SDK operations on any API or network failure. `getResponse()` returns either a structured array (Pancake API error) or a raw HTML string (Pancake server-side exception), enabling differentiated error handling.

### Method
```php
public function getResponse()
```

### Parameters
No parameters required.

### Response
#### Success Response
- Returns the API response, which can be an array (for structured errors) or a string (for raw HTML errors).

### Request Example
```php
<?php
use 
Pancake\Server;
use 
Pancake\Invoices;
use 
Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "INVALID_ID");

} catch (ApiException $e) {
    $response = $e->getResponse();

    if (is_array($response)) {
        // Pancake returned a structured JSON error
        echo "API error: " . $e->getMessage() . "\n";
        // $response may contain keys: 'status', 'error', 'error_message', 'message'
        echo "Full response: \n";
        print_r($response);
    } else {
        // Pancake returned an HTML error page (e.g., PHP fatal error)
        // The message will be pre-parsed from the HTML if possible
        echo "Server-side error: " . $e->getMessage() . "\n";
        // $response contains the raw HTML for detailed debugging
        file_put_contents('/tmp/pancake-error.html', $response);
        echo "Full error saved to /tmp/pancake-error.html\n";
    }
}
?>
```
```

--------------------------------

### Invoice::save — Create a New Invoice

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Instantiate an Invoice object, configure its properties and line items, then call save() to POST it to the API. On success, the object is reloaded with the server-assigned unique_id and all computed fields.

```APIDOC
## Invoice::save — Create a New Invoice

Instantiate an `Invoice`, configure its properties and line items, then call `save()` to POST it to the API. On success, the object is reloaded with the server-assigned `unique_id` and all computed fields.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoice;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = new Invoice($server);
    $invoice->client_id   = 2;
    $invoice->description = "Web Development Services — Q2 2024";
    $invoice->notes       = "Net 30 payment terms apply.";
    $invoice->type        = "DETAILED"; // Default; also supports "LOGGED_TIME"

    // Line items — taxes can be a name, a percentage string, or a tax ID.
    $invoice->addStandardLineItem(
        "Website Redesign",  // name
        1,                   // qty
        3500.00,             // rate
        ["VAT", "10%"],      // taxes (name or percentage; created if missing)
        "Full redesign",     // description
        0                    // discount
    );
    $invoice->addFlatRateLineItem("Hosting Setup", 150.00, [], "Annual hosting fee", 0);
    $invoice->addFixedDiscountLineItem("Loyalty Discount", 100);       // $100 off
    $invoice->addPercentageDiscountLineItem("Referral Discount", 5);   // 5% off

    // Attach files (URL or local path)
    $invoice->addFile("https://example.com/assets/contract.pdf");
    $invoice->addFile("/tmp/scope-of-work.pdf");
    $invoice->addFileFromContents("Payment due within 30 days.", "terms.txt");

    $result = $invoice->save();
    // $result['unique_id'] is now populated
    echo "Created invoice: {$invoice->unique_id}\n";
    echo "Total: {$invoice->currency_symbol}{$invoice->total}\n";

} catch (ApiException $e) {
    echo "API Error: " . $e->getMessage();
    var_dump($e->getResponse());
}
```
```

--------------------------------

### ReusableInvoiceItems::get

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Fetches all pre-defined reusable line items configured in Pancake.

```APIDOC
## ReusableInvoiceItems::get — Fetch Saved Line Item Templates

`ReusableInvoiceItems::get()` returns all pre-defined reusable line items configured in Pancake, useful for populating item pickers or auto-filling invoices.

### Method
```php
public static function get(Server $server)
public static function getById(Server $server, int $id)
```

### Parameters
#### Path Parameters
- **server** (Server) - Required - The Pancake server instance.
- **id** (int) - Required - The ID of the reusable item to fetch.

### Response
#### Success Response
- Returns an array of reusable invoice items or a single reusable invoice item by ID.

### Request Example
```php
<?php
use 
Pancake\Server;
use 
Pancake\ReusableInvoiceItems;
use 
Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    // Fetch all reusable items
    $items = ReusableInvoiceItems::get($server);
    foreach ($items as $item) {
        echo "{$item['id']}: {$item['name']} — 
";
    }

    // Fetch a specific item by ID
    $item = ReusableInvoiceItems::getById($server, 3);
    echo "Item #{$item['id']}: {$item['name']}, rate={$item['rate']}, description={$item['description']}\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}
?>
```
```

--------------------------------

### Invoice::addPaymentPart — Split Invoice into Partial Payments

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

`addPaymentPart()` (and its convenience wrappers `addPercentagePaymentPart()` / `addFixedPaymentPart()`) define a payment schedule before saving a new invoice.

```APIDOC
## Invoice::addPaymentPart — Split Invoice into Partial Payments

`addPaymentPart()` (and its convenience wrappers `addPercentagePaymentPart()` / `addFixedPaymentPart()`) define a payment schedule before saving a new invoice.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoice;
use \Carbon\Carbon;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = new Invoice($server);
    $invoice->client_id = 3;

    $invoice->addStandardLineItem("Consulting", 10, 200.00, [], "10 hours @ $200", 0);

    // 50% due immediately
    $invoice->addPaymentPart(
        true,              // is_percentage
        50,                // amount (50%)
        Carbon::now(),     // due date (Carbon instance)
        "Deposit due now"  // notes
    );

    // Remaining 50% due in 30 days
    $invoice->addPaymentPart(
        true,
        50,
        Carbon::now()->addDays(30),
        "Balance due on project completion"
    );

    $result = $invoice->save();
    echo "Invoice {$result['unique_id']} created with 2-part payment schedule.\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}
```
```

--------------------------------

### Handle Pancake API Errors

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Demonstrates how to catch and differentiate between structured API errors and raw server-side exceptions thrown by the SDK. The response can be an array or an HTML string.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "INVALID_ID");

} catch (ApiException $e) {
    $response = $e->getResponse();

    if (is_array($response)) {
        // Pancake returned a structured JSON error
        echo "API error: " . $e->getMessage() . "\n";
        // $response may contain keys: 'status', 'error', 'error_message', 'message'
        echo "Full response: \n";
        print_r($response);
    } else {
        // Pancake returned an HTML error page (e.g., PHP fatal error)
        // The message will be pre-parsed from the HTML if possible
        echo "Server-side error: " . $e->getMessage() . "\n";
        // $response contains the raw HTML for detailed debugging
        file_put_contents('/tmp/pancake-error.html', $response);
        echo "Full error saved to /tmp/pancake-error.html\n";
    }
}

```

--------------------------------

### Invoices::get - Fetch All Invoices

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Retrieves all invoices from the server and returns them as an array of hydrated `Invoice` objects. Each object has properties automatically cast to their declared PHP types.

```APIDOC
## Invoices::get — Fetch All Invoices

`Invoices::get()` retrieves every invoice on the server and returns an array of hydrated `Invoice` objects with all fields auto-cast to their declared PHP types.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoices = Invoices::get($server);

    foreach ($invoices as $invoice) {
        // Read-only computed fields are available directly as properties.
        echo sprintf(
            "Invoice %s | Client %d | Status: %s | Total: %s%.2f | Paid: %s\n",
            $invoice->invoice_number,
            $invoice->client_id,
            $invoice->status,
            $invoice->currency_symbol,
            $invoice->total,
            $invoice->is_paid ? 'Yes' : 'No'
        );
    }
    // Output:
    // Invoice INV-001 | Client 4 | Status: sent | Total: $250.00 | Paid: No
    // Invoice INV-002 | Client 7 | Status: paid | Total: $1200.00 | Paid: Yes

} catch (ApiException $e) {
    $response = $e->getResponse();
    var_dump($response); // Array with Pancake error details or raw HTML on server error
}
```
```

--------------------------------

### Invoice::addPayment — Record a Payment Against an Invoice

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

`addPayment()` posts a payment record against an existing invoice and automatically reloads the invoice to reflect the updated `paid_amount` and `status`.

```APIDOC
## Invoice::addPayment — Record a Payment Against an Invoice

`addPayment()` posts a payment record against an existing invoice and automatically reloads the invoice to reflect the updated `paid_amount` and `status`.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");

    $success = $invoice->addPayment(
        500.00,             // amount
        "Stripe",           // gateway name
        time(),             // payment datetime (Unix timestamp; null = now)
        "Completed",        // payment status
        "ch_3OxABC123",     // transaction ID
        14.50,              // transaction fee
        true                // send notification email to client
    );

    if ($success) {
        echo "Payment recorded.\n";
        echo "Paid so far:  {$invoice->currency_symbol}{$invoice->paid_amount}\n";
        echo "Still owed:   {$invoice->currency_symbol}{$invoice->unpaid_amount}\n";
        echo "Status:       {$invoice->status}\n";
    }

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}
```
```

--------------------------------

### Fetch Invoices by Client ID

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Filter invoices for a specific client using Invoices::getByClientId(). This method returns an array of Invoice objects. It includes logic to check for overdue invoices.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $client_id = 5;
    $invoices = Invoices::getByClientId($server, $client_id);

    foreach ($invoices as $invoice) {
        echo "Invoice {$invoice->unique_id}: {$invoice->currency_symbol}{$invoice->total} — {$invoice->status}\n";
        if ($invoice->days_overdue > 0) {
            echo "  *** OVERDUE by {$invoice->days_overdue} day(s) ***\n";
        }
    }

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}

```

--------------------------------

### Invoices::getByUniqueId - Fetch a Single Invoice

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Retrieves a single invoice by its unique ID, providing detailed information including totals, taxes, discounts, and partial payments. Returns `null` if the invoice is not found.

```APIDOC
## Invoices::getByUniqueId — Fetch a Single Invoice

`Invoices::getByUniqueId()` retrieves a fully detailed single invoice including totals, taxes, discounts, and partial payment parts. Returns `null` if not found.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");

    if ($invoice === null) {
        echo "Invoice not found.\n";
    } else {
        echo "Invoice:       {$invoice->invoice_number}\n";
        echo "Status:        {$invoice->status}\n";
        echo "Sub-total:     {$invoice->currency_symbol}{$invoice->sub_total}\n";
        echo "Tax total:     {$invoice->currency_symbol}{$invoice->tax_total}\n";
        echo "Total:         {$invoice->currency_symbol}{$invoice->total}\n";
        echo "Paid:          {$invoice->currency_symbol}{$invoice->paid_amount}\n";
        echo "Unpaid:        {$invoice->currency_symbol}{$invoice->unpaid_amount}\n";
        echo "View URL:      {$invoice->url}\n";
    }

} catch (ApiException $e) {
    $response = $e->getResponse();
    if (is_array($response)) {
        var_dump($response);
    } else {
        echo $response; // Raw HTML from Pancake error page
    }
}
```
```

--------------------------------

### Fetch Single Invoice by Unique ID

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Retrieve a single, detailed invoice using Invoices::getByUniqueId(). Returns null if the invoice is not found. Handles potential API errors and displays detailed invoice information or raw error responses.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");

    if ($invoice === null) {
        echo "Invoice not found.\n";
    } else {
        echo "Invoice:       {$invoice->invoice_number}\n";
        echo "Status:        {$invoice->status}\n";
        echo "Sub-total:     {$invoice->currency_symbol}{$invoice->sub_total}\n";
        echo "Tax total:     {$invoice->currency_symbol}{$invoice->tax_total}\n";
        echo "Total:         {$invoice->currency_symbol}{$invoice->total}\n";
        echo "Paid:          {$invoice->currency_symbol}{$invoice->paid_amount}\n";
        echo "Unpaid:        {$invoice->currency_symbol}{$invoice->unpaid_amount}\n";
        echo "View URL:      {$invoice->url}\n";
    }

} catch (ApiException $e) {
    $response = $e->getResponse();
    if (is_array($response)) {
        var_dump($response);
    } else {
        echo $response; // Raw HTML from Pancake error page
    }
}

```

--------------------------------

### Invoice::setPaymentDetails

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Updates the gateway and transaction metadata for a specific payment part on an already-saved invoice.

```APIDOC
## Invoice::setPaymentDetails — Update an Existing Payment Part

`setPaymentDetails()` updates the gateway and transaction metadata for a specific payment part (identified by index) on an already-saved invoice.

### Method
```php
public function setPaymentDetails(int $payment_i, string $gateway, int $payment_datetime, string $payment_status, string $transaction_id, float $transaction_fee, bool $send_notification_email)
```

### Parameters
#### Path Parameters
- **payment_i** (int) - Required - zero-based part index
- **gateway** (string) - Required - The payment gateway used
- **payment_datetime** (int) - Required - Unix timestamp of the payment
- **payment_status** (string) - Required - The status of the payment (e.g., "Completed")
- **transaction_id** (string) - Required - The unique ID of the transaction
- **transaction_fee** (float) - Required - The fee associated with the transaction
- **send_notification_email** (bool) - Required - Whether to send a notification email

### Request Example
```php
<?php
use 
Pancake\Server;
use 
Pancake\Invoices;
use 
Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");

    // Update payment part index 0 (the first part)
    $success = $invoice->setPaymentDetails(
        0,                   // payment_i: zero-based part index
        "PayPal",            // gateway
        strtotime("2024-06-01"), // payment_datetime
        "Completed",         // payment_status
        "PAYID-ABC987",      // transaction_id
        2.75,                // transaction_fee
        false                // send_notification_email
    );

    echo $success ? "Payment details updated.\n" : "Update failed.\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}
?>
```

### Response
#### Success Response
- Returns `true` on success, `false` on failure.
```

--------------------------------

### Send Invoice via Email

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Sends an invoice email to the client. Can be used statically with a unique ID or on an invoice instance to reload its state. Ensure the invoice exists.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    // Static form — use when you already have the unique_id
    $sent = Invoices::send($server, "GtQrHgsE");
    echo $sent ? "Invoice sent.\n" : "Send failed.\n";

    // Instance form — use when you have an Invoice object
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");
    $sent = $invoice->send();
    echo "Last sent timestamp: {$invoice->last_sent}\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}

```

--------------------------------

### Update Invoice Payment Details

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Updates the gateway and transaction metadata for a specific payment part of an existing invoice. Ensure the invoice and payment part index are valid.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");

    // Update payment part index 0 (the first part)
    $success = $invoice->setPaymentDetails(
        0,                   // payment_i: zero-based part index
        "PayPal",            // gateway
        strtotime("2024-06-01"), // payment_datetime
        "Completed",         // payment_status
        "PAYID-ABC987",      // transaction_id
        2.75,                // transaction_fee
        false                // send_notification_email
    );

    echo $success ? "Payment details updated.\n" : "Update failed.\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}

```

--------------------------------

### Invoice::send

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Sends the invoice email to the client associated with the invoice and reloads the invoice state.

```APIDOC
## Invoice::send — Email Invoice to Client

`Invoices::send()` (static) or `$invoice->send()` (instance) sends the invoice email to the client associated with the invoice and reloads the invoice state.

### Method
```php
// Static form
public static function send(Server $server, string $unique_id)
// Instance form
public function send() : bool
```

### Parameters
#### Static Form
- **server** (Server) - Required - The Pancake server instance.
- **unique_id** (string) - Required - The unique ID of the invoice.

#### Instance Form
No parameters required.

### Response
#### Success Response
- Returns `true` if the email was sent successfully, `false` otherwise.

### Request Example
```php
<?php
use 
Pancake\Server;
use 
Pancake\Invoices;
use 
Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    // Static form — use when you already have the unique_id
    $sent = Invoices::send($server, "GtQrHgsE");
    echo $sent ? "Invoice sent.\n" : "Send failed.\n";

    // Instance form — use when you have an Invoice object
    $invoice = Invoices::getByUniqueId($server, "GtQrHgsE");
    $sent = $invoice->send();
    echo "Last sent timestamp: {$invoice->last_sent}\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}
?>
```
```

--------------------------------

### Invoices::getByClientId - Fetch Invoices for a Client

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Filters the invoice list to retrieve only those invoices associated with a specific client ID. Returns an array of `Invoice` objects.

```APIDOC
## Invoices::getByClientId — Fetch Invoices for a Client

`Invoices::getByClientId()` filters the invoice list to those belonging to a specific client, returning an array of `Invoice` objects.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $client_id = 5;
    $invoices = Invoices::getByClientId($server, $client_id);

    foreach ($invoices as $invoice) {
        echo "Invoice {$invoice->unique_id}: {$invoice->currency_symbol}{$invoice->total} — {$invoice->status}\n";
        if ($invoice->days_overdue > 0) {
            echo "  *** OVERDUE by {$invoice->days_overdue} day(s) ***\n";
        }
    }

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}
```
```

--------------------------------

### Delete Invoice by Unique ID

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Permanently removes an invoice using its unique identifier. Use with caution as this action is irreversible.

```php
<?php
use \Pancake\Server;
use \Pancake\Invoices;
use \Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $deleted = Invoices::delete($server, "GtQrHgsE");
    echo $deleted ? "Invoice deleted.\n" : "Deletion failed.\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}

```

--------------------------------

### Invoices::delete

Source: https://context7.com/pancakeapp/php-sdk/llms.txt

Permanently removes an invoice by its unique ID.

```APIDOC
## Invoices::delete — Delete an Invoice

`Invoices::delete()` permanently removes an invoice by its unique ID.

### Method
```php
public static function delete(Server $server, string $unique_id)
```

### Parameters
#### Path Parameters
- **server** (Server) - Required - The Pancake server instance.
- **unique_id** (string) - Required - The unique ID of the invoice to delete.

### Response
#### Success Response
- Returns `true` if the invoice was deleted successfully, `false` otherwise.

### Request Example
```php
<?php
use 
Pancake\Server;
use 
Pancake\Invoices;
use 
Pancake\ApiException;

require 'vendor/autoload.php';

$server = new Server("https://billing.example.com/pancake", "YOUR_API_KEY");

try {
    $deleted = Invoices::delete($server, "GtQrHgsE");
    echo $deleted ? "Invoice deleted.\n" : "Deletion failed.\n";

} catch (ApiException $e) {
    echo "Error: " . $e->getMessage();
}
?>
```
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.