gistfile1.txt

add_action( 'woocommerce_new_booking', 'wooninja_send_pending_confirmation_email', 10, 1 );

function wooninja_send_pending_confirmation_email( $booking_id ) { 
    $what_that = get_wc_booking( $booking_id ); 
    $vendor_id = $what_that->custom_fields["_booking_vendor"]; 
    $vendor_id = intval($vendor_id[0]); 

    $GLOBALS['pending_conf_vendor'] = $vendor_id;

    add_filter( 'woocommerce_email_recipient_new_booking', 'wc_send_new_booking_multiple_addresses' );
    do_action( 'woocommerce_booking_pending-confirmation', $booking_id ); 
    remove_filter( 'woocommerce_email_recipient_new_booking', 'wc_send_new_booking_multiple_addresses' );
}

function wc_send_new_booking_multiple_addresses( $recipient ) {
    global $pending_conf_vendor;

    $recipient  = rtrim( trim( $recipient ), ',' );
  
    $vendors = get_vendor_admins( $pendinf_conf_vendor );

    $new_recipients = array();
    foreach( $vendors as $vendor ) {
        $new_recipients[] = $vendor->user_email;
    }

    $recipient .= ',' . implode( ',', $new_recipients );

    return $recipient;
}