Warning: implode(): Invalid arguments passed

I inherited a project that has a lot of little issues, and seems to come down to the custom code for theme most of the time.

I have this error.

Warning: implode(): Invalid arguments passed in /var/www/wp-content/themes/smmoa/plugins/events-manager/forms/bookingform/tickets-list.php on line 48

And the code on the line is:

// get all ticket types
$tickets_allowed = array();
$ticket_types = get_field('ticket_types', 'options');
foreach($ticket_types as $ticket_type) {
	// name, membership_level
	$ticket_name = $ticket_type['name'];
	$members_only = $ticket_type['members_only'];

	if ($members_only) {
		$levels_allowed = '|' . implode('|', $ticket_type['membership_level']) . '|'; // |level1|level2|level3|
		$tickets_allowed[$ticket_name] = (strpos($levels_allowed, '|' . $member_level . '|') === false || !$has_benefits) ? false : true;

		if ($smmoa_debug) pp('ticket_name = ' . $ticket_name . ', levels allowed = ' . $levels_allowed . ', tickets_allowed = ' . $tickets_allowed[$ticket_name] . '.');

	} else {
		// availble to anyone
		$tickets_allowed[$ticket_name] = true;
	}
}

Now the warning doesn’t seem to be affecting functionality, but the implode warning is definitely affecting sales. If its a warning that is safe to ignore, what can I do to remove the warning?

Any ideas?

http://ww.wp.xz.cn/plugins/events-manager/