Error codes

HTTP	Meaning	Example
400	Invalid request / validation	Missing field, wrong format
401	Not authenticated or invalid token	Session expired
402	Payment / limit	Plan quota exceeded
403	Forbidden	Insufficient role
404	Resource not found	Wrong ID
429	Too many requests	Rate limit
500	Server error	Unexpected condition

Response body (typical)

{
  "message": "Description or field list",
  "statusCode": 400,
  "error": "Bad Request"
}