Adding commerce checkout node form to panel page

Hi,

Thanks for your great work on this module. It ticks all the boxes of what I was looking for in a pay to publish product. I only have one problem at the moment.

I created a 'Node add/edit form' panel page based on a content type that has Commerce node checkout enabled. The node has two product listing options. I expected to be able to see the listing option selector as a form element in panels > add content > form. All the other elements from the node add/edit form were there, including 'Notification of expiration form'. But I couldn't see it.

I'm thinking maybe I need to add a relationship, but I couldn't see an option that related to Commerce node checkout.

Can you help?
Thanks!!!