Images attached to a CPT

Hi,

I am trying to get the following code to work, because I have a CPTs called 'pack' , which has a lot of attached images, I want to make the images shown on the admin edit screen.

The following code works great, but only on post-type 'post', how can I change this to make it work on post-type 'pack'

<?php
add_filter( 'rwmb_meta_boxes', 'prefix_attached_images_meta_box' );
function prefix_attached_images_meta_box( $meta_boxes ) {
	$meta_boxes[] = array(
		'title'  => esc_html__( 'Attached images', 'textdomain' ),
		'fields' => array(
			array(
				'type'     => 'custom_html',
				'callback' => 'prefix_get_images',
			),
		),
	);
	return $meta_boxes;
}

function prefix_get_images() {
	$post_id = false;
	if ( isset( $_GET['post'] ) ) {
		$post_id = intval( $_GET['post'] );
	} elseif ( isset( $_POST['post_ID'] ) ) {
		$post_id = intval( $_POST['post_ID'] );
	}
	if ( ! $post_id ) {
		return '';
	}

	$attachments = get_children( array(
		'post_parent'    => $post_id,
		'post_type'      => 'attachment',
		'post_mime_type' => 'image',
		'numberposts'    => - 1,
		'post_status'    => 'any',
	) );
	if ( empty( $attachments ) ) {
		return esc_html__( 'No images attached', 'textdomain' );
	}
	$output = '';
	foreach ( $attachments as $attachment ) {
		$output .= wp_get_attachment_image( $attachment->ID, 'thumbnail' );
	}
	return $output;
}
?>