I am trying to connect to Firebase from Android Studio Assistance but getting following error despite having internet connection.
The quickest way to get around this is to create (or upgrade your project to enable Firebase) in the Firebase Console first; then connect your app through the Android Studio tool again.
This is a generic failure message so to help us investigate it would be great if you could provide the detailed error message from the Studio log. You can find this by going to 'Help > Show Log ...'.
This Error occurs when you reach total number of projects limit on FireBase which FireBase allow you to can create per FireBase account. Then FireBase not Allow you to create any more project through Android Studio. In this case you can only connect with existing projects through Android Studio.
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In my case the problem was with the account I was signed in firebase. I was signed in with my university account (which is not gmail, but uses gmail's services). After signing in with my 'gamil.com' account, the problem resolved.
In my case, I followed below steps and it worked.
Android SDK Manager > Tools > Options > [select] Force https://...
I had this message as well. However, when I went to the Firebase console I noticed that one of my project variants got uploaded. So, I ignored the error message and continued connecting to Firebase. Every time I did this it uploaded one of my variants. When all of my variants were uploaded, the error message went away.
Just sign out your gmail account from Android Studio and then re-sign in again. After this, try again connecting to the firebase. It should connect!
simply increase the project quota from firebase....it's free i was facing this issue for very long time but now issue is resolved. i think android studio should return the proper message.
来源：https://stackoverflow.com/questions/37675320/failed-to-connect-to-firebase-from-android-studio-assistant