Return a JSON body with status and optional code/message.

Suggested statuses - Ok - InsufficientFunds - Unauthorized - InvalidDigest - InvalidToken - RateLimited - TemporaryError (retryable)

Example

{ "status": "InsufficientFunds", "balance": 95.00, "currency": "USD", "code": "W001" }

Coordinate a definitive error code list with TS (the spec references “ERRORS Codes”).