Initiate online payment with a merchant-presented QR code.
RSA SHA256 signature header. Example: Signature: algorithm=SHA256withRSA, keyVersion=0, signature=BASE64...
Rebell-assigned Client Id.
RFC3339 timestamp (e.g., 2019-05-28T12:12:00+08:00).
ORDER_CODE CGCP Amount in minor units (e.g., cents).
JSON string e.g. {"key":"value"}