Create an Invoice

POST /v1/invoices request and response.

POST /v1/invoices requires an Idempotency-Key header and this JSON body:

{
  "amount": "149.99",
  "asset": "USDT",
  "network": "TRON",
  "externalId": "ORDER-58391"
}

amount must be a positive plain decimal string with no sign, exponent, or whitespace. The response contains invoiceId, externalId, status, checkoutUrl, and expiresAt.