### Contract Payment Methods for TransferIntent

Source: https://github.com/xer-on/commerce-onchain-payment-protocol/blob/master/README.md

Details the various methods available for a frontend to select when paying a `TransferIntent`, depending on settlement token, input token, and payer's token movement allowance. These methods cover direct transfers, wrapped token handling, and Uniswap V3-based swaps.

```APIDOC
transferNative: The merchant wants ETH and the payer wants to pay ETH
transferToken: The merchant wants a token and the payer wants to pay with that token. Uses Permit2 for token movement.
transferTokenPreApproved: Same as transferToken, except the Transfers contract is directly approved by the payer for the payment token
wrapAndTransfer: The merchant wants WETH and the payer wants to pay ETH
unwrapAndTransfer: The merchant wants ETH and the payer wants to pay WETH
unwrapAndTransferPreApproved: Same as unwrapAndTransfer, except the Transfers contract is directly approved by the payer for WETH
swapAndTransferUniswapV3Native: The merchant wants a token and the payer wants to pay ETH. The token must have sufficient liquidity with ETH on Uniswap V3.
swapAndTransferUniswapV3Token: The merchant wants either ETH or a token and the payer wants to pay with a different token. The payment token must have sufficient liquidity with the settlement token on Uniswap V3.
swapAndTransferUniswapV3TokenPreApproved: Same as swapAndTransferUniswapV3Token, except the Transfers contract is directly approved by the payer for the payment token
```

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

### APIDOC: TransferIntent Solidity Struct Definition

Source: https://github.com/xer-on/commerce-onchain-payment-protocol/blob/master/README.md

Defines the structure for a TransferIntent, a primitive used for individual payments within the Coinbase Commerce Onchain Payment Protocol. This struct specifies all necessary details for a payment, including merchant, payer, currency, amount, deadline, and operator information. It must be signed by the operator to prevent forgery and data modification.

```APIDOC
TransferIntent (Solidity struct):
  - merchant's address: address
  - currency the merchant wishes to receive: address (token address)
  - amount of that currency the merchant wishes to receive: uint256
  - deadline by which the payment must be made: uint256 (timestamp)
  - payer's address: address
  - chain the payer will pay on: uint256 (chain ID)
  - address any refund should be directed to: address
  - operator who is facilitating the payment: address
  - fee the operator should receive: uint256
  - unique identifier for identifying the payment: bytes32
  - signature from the operator: bytes
  - optional signature prefix from the operator: bytes
```

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

### Payment Transaction Results and Error Handling

Source: https://github.com/xer-on/commerce-onchain-payment-protocol/blob/master/README.md

Describes the `Transferred` event emitted upon successful payment, detailing its parameters, and outlines the general approach to error handling where specific error types are returned.

```APIDOC
Transferred Event: Emitted by the contract upon successful payment with details about:
  - The operator address
  - The unique id of the TransferIntent
  - The merchant (recipient) address
  - The payer (sender) address
  - The input token that was spent by the payer
  - The amount of the input token spent by the payer
Error Handling: In the case of errors, a specific error type is returned with details about what went wrong.
```

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