Instant payments

POST /api/v1/payments — gas-sponsored USDC transfer on Polygon.

POST /api/v1/payments
Idempotency-Key: required
{
  "to": "alice | agent:slug | pay-slug | 0x…",
  "amount": "5.00",
  "memo": "optional",
  "mandateId": "uuid when policy requires"
}

Response includes txHash. Failures: policy_denied, signer_required, mandate_required, agent_paused.