meta_query – event id
$meta_query = array( 'relation' => 'AND', array( 'key' => 'mec_event_id', 'value' => '$EVENT_ID', 'compare' => '=', 'type' => 'CHAR', ), );
$meta_query = array( 'relation' => 'AND', array( 'key' => 'mec_event_id', 'value' => '$EVENT_ID', 'compare' => '=', 'type' => 'CHAR', ), );