The method received in the request-line is known by the origin server but not supported by the target resource.
The origin server MUST generate an Allow header field in a 405 response containing a list of the target resource’s currently supported methods.
A 405 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls1.
What you can do
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Have the server’s administrator or web developer go through the website’s code to find bugs - If there’s a mistake in the website’s code, the web server might not be able to correctly answer requests from a content delivery network.
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Have the server administrator sift through the server-side logs - There are two types of server-side logs — applications logs and server logs. Application logs recount the website’s entire history, like the web pages requested by visitors and which servers it connected to. Server logs provide information about the hardware running the server, revealing details about its health and status. Sifting through both types of server-side logs could uncover any alarming information about the server or website.
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Have the server administrator check the server configuration files. - By taking a look at the web server’s configuration files. One can usually find instructions for solving unintentional redirects there.
Sources