Send Event Tickets RSVP/purchase email to multiple recipients (e.g. site admin email or custom email) -- NOTE: sends to all recipients in single email (not CC or BCC, which would be preferable)

functions.php

<?php

// From https://gist.github.com/cliffordp/74b66ceb1a15ce025e7f

// Send Event Tickets RSVP/purchase email to multiple recipients (e.g. site admin email or custom email)
// NOTE: sends to all recipients in single email (not CC or BCC, which would be preferable)
// @link: https://github.com/moderntribe/event-tickets/blob/release/122/src/Tribe/RSVP.php#L373
add_filter( 'tribe_rsvp_email_recipient', 'cliff_event_tickets_email_copy_to_admin', 30 );
function cliff_event_tickets_email_copy_to_admin( $to ) {
  $additional_recipients = array(
    get_option( 'admin_email' ), // admin's email
    // '[email protected]', // custom entry
  );
  
  if ( is_string( $to ) ) {
    $additional_recipients[] = $to;
    $to = $additional_recipients;
  } elseif ( is_array( $to ) ) {
    array_merge( $to, $additional_recipients );
  } else {
    //
  }
    
  return $to;
}