I have this error:
Error:Error converting bytecode to dex: Cause: com.android.dex.DexException: Multiple dex files define Lcom/google/android/gms/common/api/zza;
I am not getting how to solve this, please help.

I don't know whether to include some lib or what
The problems of
Multiple dex files defineusually arise when you have duplicate dependency entry in your appbuild.gradle. In this case, you have a duplicate Firebase dependencies.You need to use the same version either
9.0.2or9.6.1:or
Please be aware that if you use some support library version like
24.0.0there is a chance for compatibility issue with firebase. You need to use the latest of support library or find the compatible firebase version. Read more at android error while compiling com.android.support:support-v4:24.0.0