Unity Google Play Services issue

Hello there,

I'm trying to setup Google Play Services into my game, but when I download and install my app (from Google Developer Console -> Alpha APK), the button for "Show Achievements" doesn't work. When I press it nothing happens, no login screen, no google play window, nothing.

I paste you here my code, I hope you can help me, because I'm becoming crazy with this (the button "Achievement" in my game calls the method "ShowAchievements()" in this script):

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using GooglePlayGames;
 using GooglePlayGames.BasicApi;
 using UnityEngine.SocialPlatforms;

 public class AchievementManager : MonoBehaviour {

 public static AchievementManager instance;

 // Use this for initialization
 void Awake () {
     if (instance == null)
     {
         instance = this;
     }
 }

 void Start()
 {
     PlayGamesClientConfiguration config = new PlayGamesClientConfiguration.Builder().Build();

     PlayGamesPlatform.InitializeInstance(config);
     // recommended for debugging:
     PlayGamesPlatform.DebugLogEnabled = true;
     // Activate the Google Play Games platform
     PlayGamesPlatform.Activate();
 }

 public void Login()
 {
     Social.localUser.Authenticate((bool success) => {});
 }

 public void ShowAchievements()
 {
     Login();
     Social.ShowAchievementsUI();
 }
 }

I know that there can be other things creating this issue, like SHA1, PlayConsole configuration, etc. I just want to know if there is something wrong in my code.