HTTP Status Codes for an Unsuccessful Request

These are the possible values you can receive for a status, reason, and details block depending on the HTTP status code:
HTTP Status Codes
HTTP Status Code
(part of HTTP header)
Status
Reason
Details (an array with 0 to many blocks)
400
INVALID_REQUEST
INVALID_REQUEST
Field contains the name of the field that is missing or incorrect:
Reason – MISSING_FIELD, INVALID_DATA
403
UNAUTHORIZED
UNAUTHORIZED
404
NOT_FOUND
NOT_FOUND
422
VALIDATION_ERROR
PRODUCT_INACTIVE
INVALID_MERCHANT_CONFIGURATION
PRODUCT_NOT_CONFIGURED
502
SERVER_ERROR
SYSTEM_ERROR
SERVER_TIMEOUT
SERVICE_TIMEOUT