REST API – Ordering by ACF Date field

Hello, I am having problems ordering users by an ACF datepicker field.

Datepicker return format is Ymd.

I don’t have problems ordering fields that aren’t a date.

My code is:

function order_rest_user_query($query_vars, $request) {
        $orderby = $request->get_param('orderby');
        if (isset($orderby) && $orderby === 'activo') {
            $query_vars["orderby"] = "meta_value";
            $query_vars["meta_key"] = "activo";
        }
        if (isset($orderby) && $orderby === 'fecha_alta') {
            $query_vars["orderby"] = "meta_value_num";
            $query_vars["meta_key"] = "fecha_alta";
        }
        return $query_vars;
    }
    
    add_filter( 'rest_user_query', 'order_rest_user_query', 10, 2);

The endpoint I am using is:

https://xxxxx/wp-json/wp/v2/users?context=edit&page=1&per_page=10&orderby=fecha_alta&order=asc

I have tested a lot of things with different order as result but aren’t right:

A lot of thanks.

Regards