Can not send data to PHP Server

Hello kind strangers,

I am working on a school project and we need to make a math game. I am very close. There is one problem left that me and another student can't find the solution for. We need to post the Sum, the Answer, the GameId and the UserId to our PHP server. This will later be used for evaluating. The problem is with posting the sum. We are getting this error:

NullReferenceException UnityEngine.MonoBehaviour.StartCoroutine (IEnumerator routine) (at C:/buildslave/unity/build/artifacts/generated/common/runtime/MonoBehaviourBindings.gen.cs:62) Answer.WrongAnswer (Int32 answer) (at Assets/Answer.cs:63) MoveCamera.Update () (at Assets/MoveCamera.cs:27)

MoveCamera script:

public class MoveCamera : MonoBehaviour {

 public Vector3 position = new Vector3();

 public float Speed = 0.3f;

 Answer answer = new Answer();
 GenerateSum SumGen = new GenerateSum();
 bool wrongAnswer = false;
 // Use this for initialization
 void Start () {
     
 }
 
 // Update is called once per frame
 void Update () {
     transform.position = Vector3.Lerp(transform.position, new Vector3(-110, 93.5f, (float)255.78), Speed * Time.deltaTime);
     if(transform.position.x < -100f)
     {
         if(!wrongAnswer)
         {
             answer.WrongAnswer(0);
             wrongAnswer = true;
         }
     }
     if(transform.position.x < -102f)
     {
         SumGen.Generate();
         wrongAnswer = false;
     }
 }

}

Answer script code: void OnTriggerEnter(Collider collider) { var answer = gameObject.GetComponentInChildren ().text; var sum = GameObject.Find("SumText").GetComponent ().text;

     List<string> numbers = Regex.Split(sum, @"\D+").ToList();
     int sumAnswer = 0;

     if (sum.Contains("+"))
     {
         sumAnswer = (Convert.ToInt32(numbers.ToArray()[0]) + Convert.ToInt32(numbers.ToArray()[1]));
     }
     else if (sum.Contains("-"))
     {
         sumAnswer = (Convert.ToInt32(numbers.ToArray()[0]) - Convert.ToInt32(numbers.ToArray()[1]));
     }
     else if (sum.Contains("/"))
     {
         sumAnswer = (Convert.ToInt32(numbers.ToArray()[0]) / Convert.ToInt32(numbers.ToArray()[1]));
     }

     if (sumAnswer == Convert.ToInt32(answer))
     {
         CorrectAnswer(Convert.ToInt32(answer));
     }
     else
     {
         WrongAnswer(Convert.ToInt32(answer));
     }

 }

 public void WrongAnswer(int answer)
 {
     Light spot = GameObject.Find("Spotlight").GetComponent<Light>();
     spot.color = new Color(200, 0, 0);
     spot.intensity = 0.009f;
     StartCoroutine(PostSum(answer, 0));
     main.SumCount += 1;
     if(main.SumCount == 10)
     {
         Debug.Break();
         main.SumCount = 0;
         Debug.Log(main.SumCount);
     }
 }

 public void CorrectAnswer(int answer)
 {
     Light spot = GameObject.Find("Spotlight").GetComponent<Light>();
     spot.color = new Color(0, 200, 0);
     spot.intensity = 0.009f;
     StartCoroutine(PostSum(answer, 1));
     main.SumCount += 1;
     if (main.SumCount == 10)
     {
         Debug.Break();
         main.SumCount = 0;
     }
 }

 public IEnumerator PostSum(int receivedAnswer, int isCorrect)
 {
     var sum = GameObject.Find("SumText").GetComponent<TextMesh>().text;
     int userId = Convert.ToInt32(GameObject.FindGameObjectWithTag("Username").name);
     WWWForm form = new WWWForm();
     form.AddField("user", userId);
     form.AddField("gameSum", sum);
     form.AddField("receivedAnswer", receivedAnswer);
     form.AddField("isCorrect", isCorrect.ToString());

     Debug.Log("user: " + userId + " GameSum: " + sum + " receivedAnswer: " + receivedAnswer + " isCorrect: " + isCorrect);

     using (UnityWebRequest www = UnityWebRequest.Post("http://localhost:8000/AnswerInsert.php", form))
     {
         yield return www.Send();
         Debug.Log(System.Text.Encoding.Default.GetString(www.downloadHandler.data));
     }
 }

It seems like our WrongAnswer function doesn't get into the Ienumerator.

Anyone who can help me?

Kindest regards