The verification ID used to create the phone auth credential is invalid in flutter

I'm trying to achieve Firebase phone auth in my flutter application, I've used packages : Firebase_core And Firebase_auth , here is the code i've use d:

          FirebaseAuth _auth = FirebaseAuth.instance;
          _auth.verifyPhoneNumber(
              phoneNumber: '+2$mobile',
              timeout: Duration(seconds: 60),
              verificationCompleted: (AuthCredential authCredential){
                var _credential = PhoneAuthProvider.credential(verificationId: actualCode, smsCode: smsCodeController.text);
                _auth.signInWithCredential(_credential).then((UserCredential result) async {
                  pr.hide();
                  setState(() {
                    status = 'Authentication successful';
                  });
//The rest of my success code
                }).catchError((e){
                  print(e);
                  Navigator.of(context).pushAndRemoveUntil(
                      MaterialPageRoute(
                          builder: (context) => Welcome()),
                          (Route<dynamic> route) => false);                
};
              },
              verificationFailed: (FirebaseAuthException  authException){
                print(authException.message);
              },
              codeSent: (String verificationId, [int forceResendingToken]){
                setState(() {
                  actualCode = verificationId;
                  status = 'Code sent';
                });
              },
              codeAutoRetrievalTimeout: (String verificationId){
                verificationId = verificationId;
                print(verificationId);
                setState(() {
                  status = 'Auto retrieval timeout';
                });
              },
              );

But i always get this error :

[firebase_auth/invalid-verification-id] The verification ID used to create the phone auth credential is invalid.

Any help ??