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

# Payment flow

> The HTTP 402-inspired request, transfer, verification, and delivery flow.

## Download handshake

<Steps>
  <Step title="Request content">
    The client requests `GET /api/paywalls/:id/download` without a payment proof.
  </Step>

  <Step title="Read the payment requirement">
    The server returns HTTP `402` with the exact network, currency, amount, recipient, and resource requirement.
  </Step>

  <Step title="Submit the transfer">
    The buyer wallet sends the exact native or configured ERC-20 transfer on the required chain.
  </Step>

  <Step title="Encode the proof">
    The client base64-encodes a JSON proof containing the scheme, transaction hash, and payer.
  </Step>

  <Step title="Retry the download">
    The client sends the proof in the `PAYMENT-SIGNATURE` header. After verification, the server returns the content and a `PAYMENT-RESPONSE` receipt.
  </Step>
</Steps>

```js Proof shape theme={null}
const proof = {
  scheme: 'onchain-tx',
  txHash: '0x...',
  payer: '0x...'
};

const header = btoa(JSON.stringify(proof));
```

## Idempotent recovery

The confirmed transaction hash and payer identify the proof. A valid proof may be reused for the same resource, recipient, token, and amount to recover an interrupted delivery. It cannot settle a different payment requirement.

<Info>
  Demo `exact` and `sandbox` proofs are available only when explicit demo mode is enabled outside production. They move no funds and never fabricate transaction hashes.
</Info>