The following are the reputedly facing HTTP error codes.
|Error Code||Error Message||Error Description|
|400||Bad Request||The Request sent from the browser could not be understand by server|
|401||Unauthorized||Wrong Username and Password|
|403||Forbidden/Access Denied||The server refused to serve the page. IP restriction and Modsecurity blocking are possible reasons|
|404||Page Not Found||The request page is not available in the server|
|502||Proxy Server time out||Response from Backend application will take more time. Can see in Apache logs|
|503||Service unavailable||Backend application server instance may be down. Can see in Apache logs|