API conventions

Base URL

Production gateway:

https://api.ucashier.ink

Test gateway:

https://api-beta.ucashier.ink

Open APIs use POST + application/json. Full URL = gateway + /api/public/....

Field names are case-sensitive; pass values according to the types declared in the parameter table.
Use a unique merchantOrderNo per transaction.
The signature source string uses fields marked Sign = Yes. The algorithm is HMAC-MD5 (see Signing).

Every API returns this envelope. code is the string "100000" on success; any other value is failure.

{
  "code": "100000",
  "message": "Success",
  "data": { },
  "requestId": "..."
}

Field	Type	Description
`code`	string	Status; "100000" means success
`message`	string	Status text
`data`	object	Business payload; may be empty when the request fails
`requestId`	string	Request id

Common error codes: see Parameter lookup.