Dev Docs Example: WooCommerce Memberships simplified programmatic member creation

wc-memberships-create-member.php

<?php
// Automatically grant membership to a plan at registration
function sv_add_membership_at_registration( $user_id ) {

    if ( ! function_exists( 'wc_memberships' ) ) {
        return;
    }

    $args = array(
        // Enter the ID (post ID) of the plan to grant at registration
        'plan_id'	=> 253,
        'user_id'	=> $user_id,
    );

    wc_memberships_create_user_membership( $args );
}
add_action( 'user_register', 'sv_add_membership_at_registration', 15 );

Hello, do you know how to know on which page we are in this function sv_add_membership_at_registration() ?

$_SERVER[REQUEST_URI] is admin-ajax
and get_the_ID() is empty

Many thanks!