Error while testing apk file in Phone

I have an Ionic app, it is working fine in ionic serve but when i build that app to android and test that app in phone it gives the following error “firebase.js:132 GET…76767676&_method=POST&v=js-2.0.6&transport=json&suppress_status_codes=true 404 (Not Found)”.
I have installed cordova whitelist plugin, but nothing is happening.
please help me. please