Issues with EM and YOAST

Hello, I’m using Events Manager on my WordPress but after install WordPress SEO Yoast, and put custom metadata, it gives me this error when I call the events’ page:
Fatal error: Call to a member function get_bookings() on a non-object in /home/content/69/9542969/html/grancapodanno/wp-content/themes/grancapodanno/single-event.php on line 39

On line 39 we have the following code:

$tickets_count = count($EM_Event->get_bookings()->get_tickets()->tickets);

What happen? How can I fix?

Thank you

https://www.ads-software.com/plugins/events-manager/