ticket_id_export.php

<?php

/**
 * Event Tickets: Attendees Report: CSV Export: Add Ticket ID (a.k.a. Attendee
 * ID) column to the CSV Export.
 *
 * @link https://gist.github.com/cliffordp/a3c9da35e1b4e7ca2236374c802359eb
 */
add_action( 'tribe_events_tickets_generate_filtered_attendees_list', 'tec_extend_ticket_export' );
function tec_extend_ticket_export( $event_id ) {

	if ( ! is_admin() ) {
		return;
	}

	add_filter( 'tribe_events_tickets_attendees_csv_export_columns', 'tec_add_ticket_id_column' );
	add_filter( 'tribe_events_tickets_attendees_table_column', 'tec_populate_ticket_id_column', 10, 3 );
}

function tec_add_ticket_id_column( $columns ) {

	if ( ! is_admin() ) {
		return $columns;
	}

	$columns['ticket_id'] = 'Ticket ID';

	return $columns;
}

function tec_populate_ticket_id_column( $existing, $item, $column ) {

	if ( ! is_admin() ) {
		return $existing;
	}

	if ( 'ticket_id' == $column ) {
		return $item['attendee_id'];
	}

	return $existing;
}