Redirect To External Website

You can redirect the guest to an external website (like booking.com, airbnb.com, etc) using the hotelier_add_to_cart_from_room_list_redirect filter.

function hotelier_custom_add_to_cart_from_room_list_redirect( $url ) {
    $custom_url = 'http://example.com';

    return $custom_url;
} 
add_filter( 'hotelier_add_to_cart_from_room_list_redirect', 'hotelier_custom_add_to_cart_from_room_list_redirect' );

You can also pass the checkin/checkout dates in this way:

function hotelier_custom_add_to_cart_from_room_list_redirect( $url ) {
    $checkin  = HTL()->session->get( 'checkin' );
    $checkout = HTL()->session->get( 'checkout' );

    $custom_url = add_query_arg( array(
		'checkin'  => sanitize_text_field( $checkin ),
		'checkout' => sanitize_text_field( $checkout ),
	), 'http://example.com' );

    return $custom_url;
} 
add_filter( 'hotelier_add_to_cart_from_room_list_redirect', 'hotelier_custom_add_to_cart_from_room_list_redirect' );