A WordPress plugin that updates the REST URL to use the site URL instead of the home URL.

rest-url.php

<?php

/**
 * Custom Rest URL
 *
 * @package           CustomRestUrl
 * @author            Micah Wood
 * @copyright         Copyright 2021 by Micah Wood - All rights reserved.
 * @license           GPL2.0-or-later
 *
 * @wordpress-plugin
 * Plugin Name:       Custom Rest URL
 * Plugin URI:	      https://gist.github.com/wpscholar/d60ab5ba42a4323bdde06228124a4f62
 * Description:       A WordPress plugin that updates the REST URL to use the site URL instead of the home URL.
 * Version:           1.0
 * Requires PHP:      5.6
 * Requires at least: 5.0
 * Author:            Micah Wood
 * Author URI:        https://wpscholar.com
 * License:           GPL V2 or later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 */

add_filter(
	'rest_url',
	function ( $url, $path, $blog_id, $scheme ) {
		return get_site_url( $blog_id, trailingslashit( rest_get_url_prefix() ) . $path, $scheme );
	},
	10,
	4
);