Etsy wants you to assign a Production Partner to your print-on-demand listings. Etsy's API allows us to set a production partner on your listings, but it does not (yet) allow us to create a production partner.
We recommend you create a production partner (in the Etsy shop UI) like this:
Once you have created a production partner, choose this value in your venue settings:
Your OrbitKit-generated listings will receive this production partner value.