Add a Contact Form 7 form to a Sold out Event Espresso 4 event. This is useful if you want to capture names and contact info from people that want to be signed up for a waiting list.

functions.php

<?php //Please do not include the opening PHP tag if you already have one.

// Display a contact form 7 form when the event is sold out
// to be used as a waiting list
function ee_contact_form_7_waitlist( $EVT_ID, $event ) {
    //Check the status of the event.
    $status = $event instanceof EE_Event ? $event->get_active_status() : 'inactive';

    //If the event is sold out output the contact form 7 form.
	if ( ee_espresso_clean_event_status( $event ) == 'DTS' ) {
    //The shortcode within the single quotes will be specific for your form.
		echo do_shortcode('[contact-form-7 id="107" title="EE Waitlist"]');
	}
}
add_action( 'AHEE__ticket_selector_chart__template__after_ticket_selector', 'ee_contact_form_7_waitlist', 10, 2 );