Adding spaces available on the event listing page

example.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_action( 
    'AHEE_event_details_before_the_content', 
    'ee_add_spaces_available_to_event_pages', 
    10 
);
function ee_add_spaces_available_to_event_pages( $post ) {
  $event = $post->EE_Event;
  if ( $event instanceof EE_Event ) {
    if ( ! $event->is_sold_out() && $event->is_upcoming() ) {
      $html = '<div class="spaces-available">';
      $html .= 'Spaces Still Available: ';
      $html .= $event->spaces_remaining_for_sale();
      $html .= '</div>';
      echo $html;
    }
  }
}