Q:

Unable To Write Data to Firebase Database via Unity

So recently I have been trouble trying to write/read data on the Firebase via Unity. I have had experience with working with Firebase on Java(in Android Studio), and I am currently getting to know how to use it on Unity in C#.
I did have an error before where I could not get a handshake to the firebase database and this solved kind of solved my problem, which leads me to this error I am getting.
So currently I'm using Unity 2018.2.10f1
and the Firebase SDK 5.3.0 and the quick-start from Github.
The Error I'm getting is
EntryPointNotFoundException: SWIGRegisterExceptionCallbacks_DatabaseInternal

Firebase.Database.Internal.DatabaseInternalPINVOKE+SWIGExceptionHelper..cctor ()
Rethrow as TypeInitializationException: An exception was thrown by the type initializer for SWIGExceptionHelper
Firebase.Database.Internal.DatabaseInternalPINVOKE..cctor ()
Rethrow as TypeInitializationException: An exception was thrown by the type initializer for Firebase.Database.Internal.DatabaseInternalPINVOKE
Firebase.Database.Internal.InternalFirebaseDatabase.GetInstance (Firebase.FirebaseApp app, System.String url)
Firebase.Database.FirebaseDatabase.GetInstance (Firebase.FirebaseApp app, System.String url)
Firebase.Database.FirebaseDatabase.GetInstance (Firebase.FirebaseApp app)
Firebase.Database.FirebaseDatabase.get_DefaultInstance ()
Firebase.Sample.Database.UIHandler.StartListener () (at Assets/Firebase/Sample/Database/UIHandler.cs:75)
Firebase.Sample.Database.UIHandler.InitializeFirebase () (at Assets/Firebase/Sample/Database/UIHandler.cs:71)
Firebase.Sample.Database.UIHandler.<Start>m__0 (System.Threading.Tasks.Task`1 task) (at Assets/Firebase/Sample/Database/UIHandler.cs:55)
System.Threading.Tasks.Task`1+<ContinueWith>c__AnonStorey0[Firebase.DependencyStatus].<>m__0 (System.Threading.Tasks.Task t)
System.Threading.Tasks.Task+<ContinueWith>c__AnonStorey2.<>m__0 (System.Threading.Tasks.Task t)
System.Threading.Tasks.Task+<ContinueWith>c__AnonStorey0`1+<ContinueWith>c__AnonStorey1[System.Int32].<>m__0 ()

This occurs when trying to write Data in the firebase database.
And here is my rules setting in the database : 
{
  "rules": {
    ".read": true,
    ".write": true
  }
}

The script :
// Copyright 2016 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

namespace Firebase.Sample.Database {
  using Firebase;
  using Firebase.Database;
  using Firebase.Unity.Editor;
  using System;
  using System.Collections;
  using System.Collections.Generic;
  using UnityEngine;

  // Handler for UI buttons on the scene.  Also performs some
  // necessary setup (initializing the firebase app, etc) on
  // startup.
  public class UIHandler : MonoBehaviour {

    ArrayList leaderBoard = new ArrayList();
    Vector2 scrollPosition = Vector2.zero;
    private Vector2 controlsScrollViewVector = Vector2.zero;

    public GUISkin fb_GUISkin;

    private const int MaxScores = 5;
    private string logText = "";
    private string email = "";
    private int score = 100;
    private Vector2 scrollViewVector = Vector2.zero;
    protected bool UIEnabled = true;

    const int kMaxLogSize = 16382;
    DependencyStatus dependencyStatus = DependencyStatus.UnavailableOther;

    // When the app starts, check to make sure that we have
    // the required dependencies to use Firebase, and if not,
    // add them if possible.
    protected virtual void Start() {
      leaderBoard.Clear();
      leaderBoard.Add("Firebase Top " + MaxScores.ToString() + " Scores");

      FirebaseApp.CheckAndFixDependenciesAsync().ContinueWith(task => {
        dependencyStatus = task.Result;
        if (dependencyStatus == DependencyStatus.Available) {
          InitializeFirebase();
        } else {
          Debug.LogError(
            "Could not resolve all Firebase dependencies: " + dependencyStatus);
        }
      });
    }

    // Initialize the Firebase database:
    protected virtual void InitializeFirebase() {
      FirebaseApp app = FirebaseApp.DefaultInstance;
      // NOTE: You'll need to replace this url with your Firebase App's database
      // path in order for the database connection to work correctly in editor.
      app.SetEditorDatabaseUrl("https://unity-master-server-test.firebaseio.com/");
      if (app.Options.DatabaseUrl != null)
        app.SetEditorDatabaseUrl(app.Options.DatabaseUrl);
      StartListener();
    }

    protected void StartListener() {
      FirebaseDatabase.DefaultInstance
        .GetReference("Leaders").OrderByChild("score")
        .ValueChanged += (object sender2, ValueChangedEventArgs e2) => {
          if (e2.DatabaseError != null) {
            Debug.LogError(e2.DatabaseError.Message);
            return;
          }
          Debug.Log("Received values for Leaders.");
          string title = leaderBoard[0].ToString();
          leaderBoard.Clear();
          leaderBoard.Add(title);
          if (e2.Snapshot != null && e2.Snapshot.ChildrenCount > 0) {
            foreach (var childSnapshot in e2.Snapshot.Children) {
              if (childSnapshot.Child("score") == null
              || childSnapshot.Child("score").Value == null) {
                Debug.LogError("Bad data in sample.  Did you forget to call SetEditorDatabaseUrl with your project id?");
                break;
              } else {
                Debug.Log("Leaders entry : " +
                childSnapshot.Child("email").Value.ToString() + " - " +
                childSnapshot.Child("score").Value.ToString());
                leaderBoard.Insert(1, childSnapshot.Child("score").Value.ToString()
                + "  " + childSnapshot.Child("email").Value.ToString());
              }
            }
          }
        };
    }

    // Exit if escape (or back, on mobile) is pressed.
    protected virtual void Update() {
      if (Input.GetKeyDown(KeyCode.Escape)) {
        Application.Quit();
      }
    }

    // Output text to the debug log text field, as well as the console.
    public void DebugLog(string s) {
      Debug.Log(s);
      logText += s + "\n";

      while (logText.Length > kMaxLogSize) {
        int index = logText.IndexOf("\n");
        logText = logText.Substring(index + 1);
      }

      scrollViewVector.y = int.MaxValue;
    }

    // A realtime database transaction receives MutableData which can be modified
    // and returns a TransactionResult which is either TransactionResult.Success(data) with
    // modified data or TransactionResult.Abort() which stops the transaction with no changes.
    TransactionResult AddScoreTransaction(MutableData mutableData) {
      List<object> leaders = mutableData.Value as List<object>;

      if (leaders == null) {
        leaders = new List<object>();
      } else if (mutableData.ChildrenCount >= MaxScores) {
        // If the current list of scores is greater or equal to our maximum allowed number,
        // we see if the new score should be added and remove the lowest existing score.
        long minScore = long.MaxValue;
        object minVal = null;
        foreach (var child in leaders) {
          if (!(child is Dictionary<string, object>))
            continue;
          long childScore = (long)((Dictionary<string, object>)child)["score"];
          if (childScore < minScore) {
            minScore = childScore;
            minVal = child;
          }
        }
        // If the new score is lower than the current minimum, we abort.
        if (minScore > score) {
          return TransactionResult.Abort();
        }
        // Otherwise, we remove the current lowest to be replaced with the new score.
        leaders.Remove(minVal);
      }

      // Now we add the new score as a new entry that contains the email address and score.
      Dictionary<string, object> newScoreMap = new Dictionary<string, object>();
      newScoreMap["score"] = score;
      newScoreMap["email"] = email;
      leaders.Add(newScoreMap);

      // You must set the Value to indicate data at that location has changed.
      mutableData.Value = leaders;
      return TransactionResult.Success(mutableData);
    }

    public void AddScore() {
      if (score == 0 || string.IsNullOrEmpty(email)) {
        DebugLog("invalid score or email.");
        return;
      }
      DebugLog(String.Format("Attempting to add score {0} {1}",
        email, score.ToString()));

      DatabaseReference reference = FirebaseDatabase.DefaultInstance.GetReference("Leaders");

      DebugLog("Running Transaction...");
      // Use a transaction to ensure that we do not encounter issues with
      // simultaneous updates that otherwise might create more than MaxScores top scores.
      reference.RunTransaction(AddScoreTransaction)
        .ContinueWith(task => {
          if (task.Exception != null) {
            DebugLog(task.Exception.ToString());
          } else if (task.IsCompleted) {
            DebugLog("Transaction complete.");
          }
        });
    }

    // Render the log output in a scroll view.
    void GUIDisplayLog() {
      scrollViewVector = GUILayout.BeginScrollView(scrollViewVector);
      GUILayout.Label(logText);
      GUILayout.EndScrollView();
    }

    // Render the buttons and other controls.
    void GUIDisplayControls() {
      if (UIEnabled) {
        controlsScrollViewVector =
            GUILayout.BeginScrollView(controlsScrollViewVector);
        GUILayout.BeginVertical();
        GUILayout.BeginHorizontal();
        GUILayout.Label("Email:", GUILayout.Width(Screen.width * 0.20f));
        email = GUILayout.TextField(email);
        GUILayout.EndHorizontal();

        GUILayout.Space(20);

        GUILayout.BeginHorizontal();
        GUILayout.Label("Score:", GUILayout.Width(Screen.width * 0.20f));
        int.TryParse(GUILayout.TextField(score.ToString()), out score);
        GUILayout.EndHorizontal();

        GUILayout.Space(20);

        if (!String.IsNullOrEmpty(email) && GUILayout.Button("Enter Score")) {
          AddScore();
        }

        GUILayout.Space(20);

        if (GUILayout.Button("Go Offline")) {
          FirebaseDatabase.DefaultInstance.GoOffline();
        }

        GUILayout.Space(20);

        if (GUILayout.Button("Go Online")) {
          FirebaseDatabase.DefaultInstance.GoOnline();
        }

        GUILayout.EndVertical();
        GUILayout.EndScrollView();
      }
    }

    void GUIDisplayLeaders() {
      GUI.skin.box.fontSize = 36;
      scrollPosition = GUILayout.BeginScrollView(scrollPosition, false, true);
      GUILayout.BeginVertical(GUI.skin.box);

      foreach (string item in leaderBoard) {
        GUILayout.Label(item, GUI.skin.box, GUILayout.ExpandWidth(true));
      }

      GUILayout.EndVertical();
      GUILayout.EndScrollView();
    }

    // Render the GUI:
    void OnGUI() {
      GUI.skin = fb_GUISkin;
      if (dependencyStatus != DependencyStatus.Available) {
        GUILayout.Label("One or more Firebase dependencies are not present.");
        GUILayout.Label("Current dependency status: " + dependencyStatus.ToString());
        return;
      }
      Rect logArea, controlArea, leaderBoardArea;

      if (Screen.width < Screen.height) {
        // Portrait mode
        controlArea = new Rect(0.0f, 0.0f, Screen.width, Screen.height * 0.5f);
        leaderBoardArea = new Rect(0, Screen.height * 0.5f, Screen.width * 0.5f, Screen.height * 0.5f);
        logArea = new Rect(Screen.width * 0.5f, Screen.height * 0.5f, Screen.width * 0.5f, Screen.height * 0.5f);
      } else {
        // Landscape mode
        controlArea = new Rect(0.0f, 0.0f, Screen.width * 0.5f, Screen.height);
        leaderBoardArea = new Rect(Screen.width * 0.5f, 0, Screen.width * 0.5f, Screen.height * 0.5f);
        logArea = new Rect(Screen.width * 0.5f, Screen.height * 0.5f, Screen.width * 0.5f, Screen.height * 0.5f);
      }

      GUILayout.BeginArea(leaderBoardArea);
      GUIDisplayLeaders();
      GUILayout.EndArea();

      GUILayout.BeginArea(logArea);
      GUIDisplayLog();
      GUILayout.EndArea();

      GUILayout.BeginArea(controlArea);
      GUIDisplayControls();
      GUILayout.EndArea();
    }
  }
}

A:

I have received the same error in While using Firebase.database. Go to your Inspector
Search For 
Firebase.Database . You may found 3 Firebase.Database in unity Inspector.
Found  the Firebase.database in  plugins/ios.
enable the Editor support and  ios
and save it. and deselect the  editor support and ios in  another 2 firebase.database.
and save it.
your error will be solved.

