For Content Management Systems like WordPress, deactivate plugins that might modify HTTP headers.
Knowing this can help me provide specific troubleshooting steps for your 406 error. 406 Not Acceptable - HTTP - MDN Web Docs 406 mp4
The server may reject requests from specific browsers or user agents that it considers "not acceptable". Troubleshooting and Solutions For Content Management Systems like WordPress
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 406 mp4