Google play services : login failed / application is pausing ... disconnects the RMTP client / Authentication failed.

Hi guys in a simple way I can say that login may fail for many reasons
1. Leaderboard id not matched
2. Authentication SHA1 code not matched
3. Choose Wrong Alias (in keystroke key and value stored)

NOTE: to solve 1st and 3rd problem, Just check the id or key and alias of the keystroke
NOTE: to solve 2nd problem you have to change SHA1 code from upload signed key to App signed key in Google Play Console

Steps :
1. Login to Google play console
2. Goto

3. Select your app from the right side

4. Goto 'Release Management' > 'App signing'(sub-option).
 -  In this, you found two Authentication certificate 'App signing certificate' and 'Upload certificate'
 -  Now copy App signing certificate' > SHA-1 code

5. Goto this URL Google API Console

6. Select your project (from the upper left side with three-dot) and goto 'Credential' and select your app name.

7. Change the 'Signing-certificate fingerprint' code to copied code from the 4th step.

8. DON'T FORGET TO SAVE THE CHANGES. 

So that's it. Your problem is solved. Best of luck.