facebook acces note 出来 null.what to do? 已将生成的 haskey 提供给 developer.facebook.com 但令牌仍为 null

如何解决facebook acces note 出来 null.what to do? 已将生成的 haskey 提供给 developer.facebook.com 但令牌仍为 null

    //facebook login method        
    
    Future<MyUser> signInWithFacebook() async {
                final facebookLogin = FacebookLogin();
                final result = await facebookLogin.logIn(['email']);
                var token=result.accesstoken;
        
              //printing 
//null        
        
        print('----------------------access token is :  $token');
            // not going to if condition because acesstoken is null
                if (result.accesstoken != null)
                //   if(result.status==FacebookLoginStatus.loggedIn)
                {
                  print('-----------  ${result.accesstoken}');
                  final authResult = await _firebaseAuth.signInWithCredential(
                      FacebookAuthProvider.credential(result.accesstoken.token));
                  return _userFromFirebase(authResult.user);
                } else {

// 抛出平台异常( //
代码：“ERenter code hereROR_ABORTED BY USER”， //
消息：“登录被用户中止”， ); } }