API key not valid

I'm learning firebase through Firebase Android Codelab - Build Friendly Chat
I've done all coding according to instruction till the end of Enable Authentication section.
But when trying to test the app I encounter with the following message:
`2021-11-13 09:42:17.083 4741-4741/? E/AuthUI: A sign-in error occurred.
com.google.firebase.FirebaseException: An internal error has occurred. [ API key not valid. Please pass a valid API key. ]
at com.google.android.gms.internal.firebase-auth-api.zzto.zza(com.google.firebase:firebase-auth@@21.0.1:4)
at com.google.android.gms.internal.firebase-auth-api.zzuw.zza(com.google.firebase:firebase-auth@@21.0.1:9)
at com.google.android.gms.internal.firebase-auth-api.zzux.zzl(com.google.firebase:firebase-auth@@21.0.1:1)
at com.google.android.gms.internal.firebase-auth-api.zzuu.zzk(com.google.firebase:firebase-auth@@21.0.1:25)
at com.google.android.gms.internal.firebase-auth-api.zztl.zzh(com.google.firebase:firebase-auth@@21.0.1:1)
at com.google.android.gms.internal.firebase-auth-api.zzoj.zza(com.google.firebase:firebase-auth@@21.0.1:2)
at com.google.android.gms.internal.firebase-auth-api.zzvb.zza(com.google.firebase:firebase-auth@@21.0.1:23)
at com.google.android.gms.internal.firebase-auth-api.zzul.zza(com.google.firebase:firebase-auth@@21.0.1:4)
at com.google.android.gms.internal.firebase-auth-api.zzpt.zzq(com.google.firebase:firebase-auth@@21.0.1:4)
at com.google.android.gms.internal.firebase-auth-api.zztp.zzl(com.google.firebase:firebase-auth@@21.0.1:5)
at com.google.android.gms.internal.firebase-auth-api.zzql.zzd(com.google.firebase:firebase-auth@@21.0.1:3)
at com.google.android.gms.internal.firebase-auth-api.zzqk.accept(Unknown Source:6)
at com.google.android.gms.common.api.internal.zacj.doExecute(com.google.android.gms:play-services-base@@17.5.0:2)
at com.google.android.gms.common.api.internal.zah.zaa(com.google.android.gms:play-services-base@@17.5.0:9)
at com.google.android.gms.common.api.internal.GoogleApiManager$zaa.zac(com.google.android.gms:play-services-base@@17.5.0:193)
at com.google.android.gms.common.api.internal.GoogleApiManager$zaa.zab(com.google.android.gms:play-services-base@@17.5.0:158)
at com.google.android.gms.common.api.internal.GoogleApiManager$zaa.zaa(com.google.android.gms:play-services-base@@17.5.0:126)
at com.google.android.gms.common.api.internal.GoogleApiManager.handleMessage(com.google.android.gms:play-services-base@@17.5.0:164)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:214)
at android.os.HandlerThread.run(HandlerThread.java:67)
`
It seems the the API key given in mock-google-services.json has expired.
What's the solution for this issue?