onRegisterButtonClick.dart

Future<void> _onRegisterButtonClick() async {
    showProgressBar(context, "Requesting OTP...");
    this._phoneNo = _countryCode + _numberController.text;

    final PhoneVerificationCompleted verificationCompleted =
        (FirebaseUser user) {
      _navigateToHome();
    };

    final PhoneVerificationFailed verificationFailed =
        (AuthException authException) {
      Navigator.pop(context);
      switch (authException.code) {
        case 'invalidCredential':
          showSnackBar(_scaffoldKey, 'Incorrect phone number...');
          break;
        case 'quotaExceeded':
          showSnackBar(_scaffoldKey, 'Quota Exceeded for this number...');
          break;
      }
    };

    final PhoneCodeSent codeSent =
        (String verificationId, [int forceResendingToken]) async {
      this._verificationId = verificationId;
      Navigator.pop(context);
      setState(() {
        _isOtpFieldVisible = true;
      });
    };

    final PhoneCodeAutoRetrievalTimeout codeAutoRetrievalTimeout =
        (String verificationId) {
      this._verificationId = verificationId;
    };

    await _auth.verifyPhoneNumber(
        phoneNumber: _phoneNo,
        timeout: const Duration(seconds: 0),
        verificationCompleted: verificationCompleted,
        verificationFailed: verificationFailed,
        codeSent: codeSent,
        codeAutoRetrievalTimeout: codeAutoRetrievalTimeout);
  }