Adding post ID as a field

Hey,

I'm trying to add the post id as a field value to a field in a field group that I have already set up using the UI.

Here is my code which I'm running on every page at plugins_loaded, but it's not working. Can you help?

add_filter( 'rwmb_meta_boxes', function ( $meta_boxes ) {
    $postID = null;
    if ( isset( $_GET['post'] ) ) {
    $postID = intval( $_GET['post'] );
} elseif ( isset( $_POST['post_ID'] ) ) {
    $postID = intval( $_POST['post_ID'] );
}
    $meta_boxes[] = [
        'title'      => 'Orders',
        'post_types' => 'Order',
        'fields'     => [
            [
                'name' => 'Order ID',
                'id'   => 'orderID',
                'type' => 'number',
                'std' => $postID,            
                ],
        ],
    ];
    return $meta_boxes;
} );