query on a join table

ForumPostsTable.php

<?php
//Model ForumPostsTable : 
		$this->belongsToMany('Subscribers', [
			'className'		=> 'Users',
			'targetForeignKey'	=> 'user_id',
            'joinTable'  	=> 'forum_posts_subscribers',
            'dependent' 	=> true,
        ]);


//Later
	public function replyNotify($data = null)
	{
		$result = false;
		if(isset($data) && isset($data['forum_post_id']) && isset($data['exception']) && is_array($data['exception'])) {
			//Récupération de tous les abonnés;
			$query = $this->ForumPostsSubscribers->findByForumPostId($data['forum_post_id']);
			$subscribers = $query->toArray();
			
			$result = $Subscribers;
			// $result = true;
		}
		return $result;
	}

//Got an error : 
Table "App\Model\Table\ForumPostsTable" is not associated with "ForumPostsSubscribers"
  
//and if I try :
  $query = $this->ForumPostsSubscribers->findByForumPostId($data['forum_post_id']);
//then got an error:
SQLSTATE[42S22]: Column not found: 1054 Unknown column 'Subscribers.forum_post_id' in 'where clause'
  
//How can I access my joinTable?