This hook is an alternative to the  ‘wp_travel_after_main_content’  hook which allows you to add your custom text  below the “Related Trip” section in single trip page.

Source

File : /templates/content-single-itineraries.php

Example :

function prefix_wp_travel_after_single_itinerary( $post_id ) {
    esc_html_e( 'This is the content added using this hook', 'text-domain' );
}
add_action( 'wp_travel_after_single_itinerary', 'prefix_wp_travel_after_single_itinerary'  );