Here is the PHP from the builder
add_filter( 'rwmb_meta_boxes', 'your_prefix_function_name' );
function your_prefix_function_name( $meta_boxes ) {
$prefix = '';
$meta_boxes[] = [
'title' => __( 'Retreat Guest Info', 'your-text-domain' ),
'id' => 'retreat-guest-info',
'post_types' => ['retreat-info'],
'storage_type' => 'custom_table',
'table' => 'wp_retreat_guest_info',
'fields' => [
[
'name' => __( 'First Name', 'your-text-domain' ),
'id' => $prefix . 'customer_first_name',
'type' => 'text',
'required' => true,
],
[
'name' => __( 'Last Name', 'your-text-domain' ),
'id' => $prefix . 'customer_last_name',
'type' => 'text',
'required' => true,
],
],
];
return $meta_boxes;
}