> ## Documentation Index
> Fetch the complete documentation index at: https://docs.conduitpay.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Verify

> Validate a payment payload before serving your resource.

`POST /api/x402/verify` validates a payment payload before you serve your resource. The `withPayment()` middleware calls this automatically.

## What gets checked

| Check            | Details                                                 |
| ---------------- | ------------------------------------------------------- |
| Payload decoding | Base64 decodes to a valid payment object                |
| Time validity    | `validAfter` has passed, `validBefore` has not expired  |
| Amount           | Meets or exceeds the required minimum                   |
| Recipient        | `to` matches your `payTo`                               |
| Nonce            | Not already used (via `authorizationState` on Arc USDC) |
| Balance          | Payer has sufficient USDC on Arc                        |

## Nonce replay protection

Every EIP-3009 authorization includes a unique `nonce`. Conduit calls `authorizationState(authorizer, nonce)` on the Arc USDC contract before processing. If the nonce was already used, Conduit rejects the payment. Replay attacks are impossible.

## Error responses

| Error                               | Meaning                         |
| ----------------------------------- | ------------------------------- |
| `Missing payload or paymentDetails` | Request body incomplete         |
| `Invalid payment payload encoding`  | Base64 decode failed            |
| `Payment not yet valid`             | `validAfter` is in the future   |
| `Payment authorization expired`     | `validBefore` has passed        |
| `Insufficient payment`              | Amount below the minimum        |
| `Wrong recipient`                   | `to` doesn't match `payTo`      |
| `Payment nonce already used`        | Authorization already submitted |
| `Insufficient USDC balance`         | Payer lacks funds on Arc        |