> ## Documentation Index
> Fetch the complete documentation index at: https://circle-devdocs-test-ai-codegen-component.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# How-to: Create an Onchain Transaction

When a payment is in the `CRYPTO_FUNDS_PENDING` state, the OFI must initiate an
onchain transaction to fulfill the payment in USDC. CPN provides an API to help
prepare and validate the onchain transaction call data, and to broadcast the
transaction and monitor its state.

## Steps

Use the following steps to create and broadcast a USDC transfer to the
blockchain:

### Step 1: Prepare the call data

Call the
[create transaction](/api-reference/cpn/cpn-platform/create-transaction)
endpoint to get an unsigned message object. Note that transaction objects differ
between EVM blockchains and Solana.

The API call must include the sender wallet information (which must be an EOA
wallet). The rest of the transaction data such as amount, chain, destination
address, and other information is populated automatically by CPN using the
payment record.

### Step 2: Create and sign the transaction

Review the unsigned message object and ensure that it matches your expectations
for the crypto transaction. Depending on the blockchain, the signing process
varies.

#### EVM

When the unsigned data has been confirmed, you must sign it in accordance with
[EIP-712](https://eips.ethereum.org/EIPS/eip-712). Next, you construct an
[EIP-3009](https://eips.ethereum.org/EIPS/eip-3009) transaction from the signed
data:

1. **Extract the signature**. Extract the signature components (`v`, `r`, `s`)
   from the signed typed data.
2. **Encode the function call**. Using the ERC-20 smart contract's ABI for the
   `TransferWithAuthorization` function, encode the function call with the
   required parameters: sender address (`from`), recipient address (`to`),
   `validAfter`, `validBefore`, `nonce`, and the signature components, `v`, `r`,
   `s`. This encoding creates the data field for the raw transaction.
3. **Construct the transaction object**. Build a raw transaction object that
   includes the target contract address (USDC), the encoded function call data,
   and other necessary parameters such as nonce, gas limit, max fee per gas, max
   priority fee per gas, and chain ID.
4. **Serialize the transaction**. Serialize the transaction object into the
   proper RLP-encoded format so that it can be signed.

The following is an example of the transaction object in
[EIP-1559](https://eips.ethereum.org/EIPS/eip-1559) format, for EIP-3009
`TransferWithAuthorization` contract execution.

```json JSON theme={null}
{
  "to": "0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238",
  "value": "0x0",
  "gasLimit": "0x5208",
  "maxPriorityFeePerGas": "0x59682f00",
  "maxFeePerGas": "0x59682f00",
  "nonce": "0x8",
  "chainId": 1,
  "type": "0x2",
  "data": "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"
}
```

Sign this transaction data and move on to the next step.

#### Solana

On Solana, the transfer data follows Solana's `Ed2559` transaction format. After
confirming the unsigned data, a transaction object is constructed with the
transfer data. You sign the transaction object and submit it to the API.

<Note>
  **Note:** Once signed, Solana transaction objects expire after one minute, so
  you should submit it immediately.
</Note>

### Step 3: Submit the signed transaction

Call the
[submit transaction](/api-reference/cpn/cpn-platform/submit-transaction)
endpoint to submit the signed transaction data to CPN. CPN broadcasts the
transaction and provides a webhook to notify you of the transaction status. This
webhook is also provided to the BFI.

Once the BFI confirms that they have received the desired amount for the
payment, the BFI initiates the fiat payment.

#### Handling failures

If a transaction fails and the payment is still valid (for example, it has not
expired), you can address the issues with the transaction and initiate a new
transaction. For example, if there was not enough gas to cover the transaction,
you could deposit additional gas tokens to the wallet, and try again.

Only one active transaction is allowed at a time per payment, so you can only
initiate a new transaction once the previous one has failed.