# HTTP Return Codes

* HTTP `4XX` return codes are used for malformed requests; the issue is on the sender's side.
* HTTP `403` return code is used when the WAF Limit (Web Application Firewall) has been violated.
* HTTP `409` return code is used when a cancelReplace order partially succeeds. (i.e. if the cancellation of the order fails but the new order placement succeeds.)
* HTTP `429` return code is used when breaking a request rate limit.
* HTTP `418` return code is used when an IP has been auto-banned for continuing to send requests after receiving `429` codes.
* HTTP `5XX` return codes are used for internal errors; the issue is on Trade.mn's side.