fb login works but invite share and challenge not working

Can anyone help me with the Facebook integration in unity for android game? After using the below script I found no error in the console so I built the apk and tested it on my phone. I can log in to Facebook from the game but the Invite and sharing options are not working also the challenge option isn't working. Is it got anything to do with the Facebook android app?

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 using System.Collections.Generic;
 using Facebook.Unity;
 
 public class Test : MonoBehaviour {
     public GameObject LoggedInUI;
     public GameObject NotLoggedInUI;
     public GameObject Friend;
     private static string applink = "https://fb.me/846500322149000";/*"http://www.mdfazlarabby.speranzabd.com/upcomingprojects"*/
     void Awake(){
         if (!FB.IsInitialized) {
             FB.Init (InitCallBack);
         }
     }
 
     void InitCallBack(){
         Debug.Log ("FB has been initiased.");
         ShowUI ();
     }
 
     public void Login(){
         if (!FB.IsLoggedIn) {
             FB.LogInWithReadPermissions (new List<string>{ "user_friends" }, LoginCallBack);
         }
     }
 
     void LoginCallBack(ILoginResult result){
         if (result.Error == null) {
             Debug.Log ("FB has logged in.");
             ShowUI ();
         } else {
             Debug.Log ("Error during login: " + result.Error);
         }
     }
 
     void ShowUI(){
         if (FB.IsLoggedIn) {
             LoggedInUI.SetActive (true);
             NotLoggedInUI.SetActive (false);
             FB.API ("me/picture?width=100&height=100", HttpMethod.GET, PictureCallBack);
             FB.API ("me?fields=first_name", HttpMethod.GET, NameCallBack);
             FB.API ("me/friends", HttpMethod.GET, FriendCallBack);
             FB.GetAppLink (AppLinkCallback);
         } else {
             LoggedInUI.SetActive (false);
             NotLoggedInUI.SetActive (true);
         }
     }
 
     void PictureCallBack(IGraphResult result){
         Texture2D image = result.Texture;
         LoggedInUI.transform.FindChild ("ProfilePicture").GetComponent<Image> ().sprite = Sprite.Create (image, new Rect (0, 0, 100, 100), new Vector2 (0.5f, 0.5f));
     }
 
     void NameCallBack(IGraphResult result){
         IDictionary<string, object> profile = result.ResultDictionary;
         LoggedInUI.transform.FindChild ("Name").GetComponent<Text> ().text = "Hi There! " + profile ["first_name"];
     }
 
     public void LogOut(){
         FB.LogOut ();
         ShowUI ();
     }
 
     public void Share(){
         FB.ShareLink (new System.Uri ("http://www.mdfazlarabby.speranzabd.com/upcomingprojects/"), "This game is awesome!", "A description of the game.", new System.Uri("http://www.mdfazlarabby.speranzabd.com/wp-content/uploads/2016/07/BullsAdventure.jpg/"),ShareCallback);
     }
 
     private void ShareCallback (IShareResult result) {
         if (result.Cancelled) {
             Debug.Log ("Share cancelled.");
         } else if (!string.IsNullOrEmpty (result.Error)) {
             Debug.Log (" Error in Share" + result.Error);
         } else {
             Debug.Log ("Share was successful" +result.RawResult);
         }
 
     }
 
     public void Invite(){
         FB.Mobile.AppInvite (new System.Uri (applink), new System.Uri ("http://www.mdfazlarabby.speranzabd.com/wp-content/uploads/2016/07/BullsAdventure.jpg/"), InviteCallback);
     }
 
     void InviteCallback( IAppInviteResult result)
     {
         if (result.Cancelled) {
             Debug.Log ("Invite cancelled.");
         } else if (!string.IsNullOrEmpty (result.Error)) {
             Debug.Log (" Error in Invite" + result.Error);
         } else {
             Debug.Log ("Invite was successful" +result.RawResult);
         }
 
 
     }
 
     public void Challenge() 
     {
         FB.AppRequest ("Custom message", null, new List<object>{ "app users" }, null, null, "Data", "Challenge Your Friends!");
     }
     void ChallengeCallback(IAppRequestResult result){
         if (result.Cancelled) {
             Debug.Log ("Challenge cancelled.");
         } else if (!string.IsNullOrEmpty (result.Error)) {
             Debug.Log (" Error in Challenge" + result.Error);
         } else {
             Debug.Log ("Challenge was successful" +result.RawResult);
         }
     
     
     }
 
 
     void FriendCallBack(IGraphResult result){
         IDictionary<string, object> data = result.ResultDictionary;
         List<object> friends = (List<object>)data ["data"];
         foreach (object obj in friends) {
             Dictionary<string, object> dictio = (Dictionary<string, object>)obj;
             CreateFriend(dictio ["name"].ToString (), dictio ["id"].ToString ());
         }
     }
 
     void CreateFriend(string name, string id){
         GameObject myFriend = Instantiate (Friend);
         Transform parent = LoggedInUI.transform.FindChild ("ListContainer").FindChild ("FriendList");
         myFriend.transform.SetParent (parent);
         myFriend.GetComponentInChildren<Text> ().text = name;
         FB.API(id + "/picture?width=100&height=100", HttpMethod.GET, delegate(IGraphResult result) {
             myFriend.GetComponentInChildren<Image>().sprite = Sprite.Create (result.Texture, new Rect (0, 0, 100, 100), new Vector2 (0.5f, 0.5f));
         });
     }
 
     void AppLinkCallback (IAppLinkResult result)
     {
         if (string.IsNullOrEmpty (result.Error)) {
             Debug.Log ("Applink done: " + result.RawResult);
             IDictionary<string, object> dictio = result.ResultDictionary;
             if (dictio.ContainsKey ("target_url")) {
                 string url = dictio ["target_url"].ToString ();
                 string keyword = "request_ids=";
                 int k = 0;
                 while (k < url.Length - keyword.Length && !url.Substring (k, keyword.Length).Equals (keyword))
                     k++;
                 k += keyword.Length;
                 int l = k;
                 while (url [l] != '&' && url [l] != '%')
                     l++;
                 string id = url.Substring (k, l - k);
                 FB.API ("/" + id + "_" + AccessToken.CurrentAccessToken.UserId, HttpMethod.GET, RequestCallback);
         } else 
         {
             Debug.Log ("Applink Error :" + result.Error);
         }
     }
 
     
 }
     void RequestCallback(IGraphResult result){
         Debug.Log ("Request callback");
         if (string.IsNullOrEmpty (result.Error)) {
             IDictionary<string, object> dictio = result.ResultDictionary;
             if (dictio.ContainsKey ("data"))
                 Debug.Log (dictio ["data"]);
             if (dictio.ContainsKey ("id"))
                 FB.API ("/" + dictio ["id"], HttpMethod.DELETE, null);
         } else {
             Debug.Log ("Error in request:" + result.Error);
         }
     }
 }