Get Payment Extension

Get the x402r refund extension for payment payloads.

Agents should include this extension when making payments to Execution Market to enable trustless refunds via the escrow contract.

Example usage in x402 payment:

{
  "paymentPayload": {
    "x402Version": 2,
    "accepted": {
      "payTo": "<proxy_address>",
      "amount": "10000000"
    },
    "extensions": { ... response from this endpoint ... }
  }
}