For Content Management Systems like WordPress, deactivate plugins that might modify HTTP headers.

The 406 error frequently arises due to a mismatch between requested and available content types, according to Error404.atomseo.com .

This paper explores the status code, a client-side error indicating that a server cannot fulfill a request based on the acceptable content types defined by the client. Understanding the 406 Not Acceptable Error

Sometimes, invalid file extensions or special characters in the URL can trigger 406 errors, as shown in this video explanation. Technical Context

A client may request JSON, but the server only offers XML, resulting in a 406.

Review mod_security logs to see if a firewall is blocking the request.

Ensure the client is requesting data types ( Accept header) that the server actually provides.