The following firebase function sends the OTP code to the phone number. Problem is.. _onVerificationCompleted gets only invoked when the phone number is on the device that is sending the request (SIM card). What if I need to know the sent otp code when the _onVerificationCompleted method will never get called as it's a different device phone number? I tried PhoneAuthProvider.credential(verificationId: verification, smsCode: enteredCode); But this method's return type is PhoneAuthCredential, which is only used when trying to signin/login the user.

I just need to verify the entered code == the smsCode without signing in. Any help would be really appreciated!

Future<void> verifyPhoneNumber({@required String phoneNumber}) async {
    await _auth.verifyPhoneNumber(
        phoneNumber: phoneNumber,
        verificationCompleted: _onVerificationCompleted,
        verificationFailed: _onVerificationFailed,
        codeSent: _onCodeSent,
        codeAutoRetrievalTimeout: _onCodeTimeout);
  }

  _onVerificationCompleted(PhoneAuthCredential authCredential) async {
    print("verification completed ${authCredential.smsCode}");
    if (otpTextFieldController.text == authCredential.smsCode) {
      print('Verified!');
    } else {
      print('not-verified!');
    }
    setState(() {
      _numberValidated = true;
    });
    if (authCredential.smsCode != null) {
      try {} on FirebaseAuthException catch (e) {
        print('OTP error : $e');
      }
      setState(() {
        isLoading = false;
      });
    }
  }

  _onVerificationFailed(FirebaseAuthException exception) {
    print('verification : ${exception}');
    if (exception.code == 'invalid-phone-number') {
      showMessage("The phone number entered is invalid!");
    }
  }

  _onCodeSent(String verificationId, int forceResendingToken) {
    this.verificationId = verificationId;
    print(forceResendingToken);
    print("code sent = ${this.verificationId}");
  }

  _onCodeTimeout(String timeout) {
    return null;
  }

  void showMessage(String errorMessage) {
    showDialog(
        context: context,
        builder: (BuildContext builderContext) {
          return AlertDialog(
            title: Text("Error"),
            content: Text(errorMessage),
            actions: [
              TextButton(
                child: Text("Ok"),
                onPressed: () async {
                  Navigator.of(builderContext).pop();
                },
              )
            ],
          );
        }).then((value) {
      setState(() {
        isLoading = false;
      });
    });
  }