Allow all IAC attendees to view protected content

example.php

<?php


add_filter( 'tribe_tickets_shortcode_can_see_content', static function( $can_see_content, $filter_args ) {

    // Only run our logic below if the user is logged in or if they cannot currently see the content.
    if ( ! is_user_logged_in() || $can_see_content ) {
        return $can_see_content;
    }

    $current_user = wp_get_current_user();

    // Check to see if there are any attendees for the ticket ID(s) for this user email.
    $args = [
        // Only get one to improve performance.
        'per_page' => 1,
        'by'       => [
            'ticket'          => $filter_args['ticket_ids'],
            // purchaser_email is actually referencing the meta key which IAC uses too.
            'purchaser_email' => $current_user->user_email,
        ],
    ];

    $attendees = Tribe__Tickets__Tickets::get_event_attendees_by_args( $filter_args['post_id'], $args );

    // Return whether they have matching attendee(s).
    return ! empty( $attendees['attendees'] );

}, 100, 2);