limit RSVP max purchases for ET

functions.php

<?php

add_filter( 'tribe_tickets_get_ticket_max_purchase', 'et_set_max_rsvp_purchase_limit', 10, 4 );

function et_set_max_rsvp_purchase_limit( $available_at_a_time, $ticket, $event, $ticket_id  ) {

	if ( $available_at_a_time <= 1 || $ticket->provider_class != 'Tribe__Tickets__RSVP' ) {
		return $available_at_a_time;
	}

	return 1;
}