ios - Firebase Phone Auth Error FIRAuthErrorCodeMissingAppToken -

i'm getting error firebase when trying sign in phone number on ios

error_name: 'error_missing_app_token', nslocalizeddescription: 'there seems problem project\'s firebase phone number authentication set-up, please make sure follow instructions found @ https://firebase.google.com/docs/auth/ios/phone-auth' }, domain: 'firautherrordomain' 

i've followed linked directions (https://firebase.google.com/docs/auth/ios/phone-auth) enable phone authentication , add apns keys, etc.

what "token" missing cause error?

thanks.