<?php
/**
* The filter is named rest_{post_type}_collection_params. So you need to hook a new filter for each
* of the custom post types you need to sort.
* @link https://www.timrosswebdevelopment.com/wordpress-rest-api-post-order/
*/
// This enables the orderby=menu_order for Posts
add_filter( 'rest_post_collection_params', 'filter_add_rest_orderby_params', 10, 1 );
// And this for a custom post type called 'portfolio'
add_filter( 'rest_portfolio_collection_params', 'filter_add_rest_orderby_params', 10, 1 );
/**
* Add menu_order to the list of permitted orderby values
*/
function filter_add_rest_orderby_params( $params ) {
$params['orderby']['enum'][] = 'menu_order';
return $params;
}