What's the Best Way to Set Up an Android Proxy for Secure Browsing? or How Do I Use an Android Proxy

Man, proxies on android can be such a pain. One thing that worked for me was clearing the cache of the app I was using.

Also, try switching between WiFi and mobile data—some ISPs block proxy traffic on cellular.

If you're still stuck, maybe test your proxy settings with a tool like Proxy Checker (just google it).