CPT to CPT with slug

I am using a CPT “ai1ec_event” created by All-in-One Event Calendar.
I need to connect an Event only to another Event that has the slug “corsi” or “seminari” or “master”. I don’t want to see in the list events with other slugs.

What I’ve done so far shows me all types od Events, even if I specify the slugs in the “to_query_vars” array.

p2p_register_connection_type( array(
    'name' => 'iscrizione_a_corso',
    'from' => 'ai1ec_event',
    'to' => 'ai1ec_event',
     'to_query_vars' => array( 'events_categories' => 'corsi ,  seminari , master' ) ,
	'reciprocal' => true ,

     'admin_box' => array(
    'show' => 'to',
    'context' => 'side'
  ),
	'title' => array(
   		'from' => __( 'Collega Corso', 'my-textdomain' ),
  ),
  'to_labels' => array(
      'singular_name' => __( 'Corso', 'my-textdomain' ),
      'search_items' => __( 'Cerca Corso', 'my-textdomain' ),
      'not_found' => __( 'Nessun Corso trovato.', 'my-textdomain' ),
      'create' => __( 'Crea Collegamento', 'my-textdomain' )
  )
	) );

Any suggestion?

https://wordpress.org/plugins/posts-to-posts/