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Reference
HTTP error codes
What the most common 4xx and 5xx errors mean, why they happen and how to fix them.
4xx: client errors
The request cannot be fulfilled as sent: a wrong address, missing credentials or no permission.
400Bad RequestThe server could not understand the request.401UnauthorizedThe request needs valid authentication.402Payment RequiredPayment is needed before the request can be completed.403ForbiddenThe server understood the request and refuses to fulfil it.404Not FoundThe server cannot find the requested page.
5xx: server errors
The request looks fine, but the server or something behind it failed to answer.
500Internal Server ErrorSomething went wrong on the server.501Not ImplementedThe server does not support what the request asks for.502Bad GatewayA gateway got an invalid response from the server behind it.503Service UnavailableThe server cannot handle the request right now.504Gateway TimeoutA gateway did not get a response from the server behind it in time.505HTTP Version Not SupportedThe server does not support the HTTP version of the request.
Looking for another code?
The HTTP status codes reference covers every code from 100 to 511, and you can check what any address returns.
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