OptionalcodeYour own transfer description — your order number, say — instead of a generated HT… code.
Letters and digits, 6 to 20, upper-cased; unused on that bank account, or the call is a 409.
Longer is safer: it is matched by looking for it inside the transfer description.
Optionalconnection_OptionalcustomerOptionaldescriptionOptionalexpires_OptionalinvoiceIssue an e-invoice once the payment succeeds.
Optionalipn_Your endpoint for this payment's IPN calls (signed with HMAC-SHA256; see verifyIpn).
OptionalmetadataYour order id: the payment's idempotency key and metadata.order_id.
Optionalreturn_
POST /paymentsfor one of your orders; seepayments.createOrder.