Recently, my websites suddenly started showing the HTTP 406 – Not Acceptable error. This issue appeared without any changes made on my end, which made it a bit confusing at first. Initial Troubleshooting After searching online, I found that many people suggested disabling the mod_security module, as it can sometimes block legitimate requests. I tried the recommended configurations to turn off mod_security, but unfortunately, that solution did not work for me. Actual Cause & Solution I then contacted my website’s hosting/server support team and explained the issue in detail. After checking their logs, they informed me that: My requests were being blocked by server security rules The affected requests were not whitelisted They removed the blocking rule / added my requests to the whitelist Once this was done, the websites started working normally again.