This filter is applied to use get the current page URL it includes one parameter.
$ajax_url -> admin url.
An example of how you can append is below:
function rpress_get_ajax_url( $ajax_url ) {
$current_url = //current page url;
$ajax_url = //amin url;
}
add_filter('rpress_ajax_url', 'rpress_get_ajax_url', 10, 1);