ET+ Fix coupon apply bug || AR page saving to empty page

functions.php

<?php
add_filter( "woocommerce_get_checkout_url", "rt_fix_maybe_filter_checkout_url_to_attendee_registration", 20);

/**
 * Hooked to the woocommerce_get_checkout_url filter to hijack URL if on cart and there
 * are attendee registration fields that need to be filled out
 *
 * @since 4.9
 *
 * @param string $checkout_url
 *
 * @return null|string
 */
function rt_fix_maybe_filter_checkout_url_to_attendee_registration( $checkout_url ) {
    $on_registration_page = tribe( 'tickets.attendee_registration' )->is_on_page();
    $shortcode_page       = tribe( 'tickets.attendee_registration' )->is_using_shortcode();
    // we only want to skip url override in our registration page
    if ( $on_registration_page || $shortcode_page ) {
        return $checkout_url;
    }
    /** @var \Tribe__Tickets_Plus__Commerce__WooCommerce__Main $commerce_woo */
    $commerce_woo = tribe( 'tickets-plus.commerce.woo' );
    $provider     = tribe_get_request_var( 'provider' );
    // Return default URL if provider is not WC
    if ( !empty( $provider ) && $commerce_woo->attendee_object !== $provider ) {
        return $checkout_url;
    }
    $cart_tickets  = tribe( 'tickets-plus.commerce.woo.cart' )->get_tickets_in_cart();
    $cart_has_meta = Tribe__Tickets_Plus__Main::instance()->meta()->cart_has_meta( $cart_tickets );
    // If cart has no meta, return checkout url
    if ( ! $cart_has_meta ) {
        return $checkout_url;
    }
    $url = add_query_arg( 'provider', $commerce_woo->attendee_object, tribe( 'tickets.attendee_registration' )->get_url() );
    return $url;
}