Hi houseraccoon ,
Thanks for your post and glad to hear you're trying to extend ATUM😉.
We have two types of ATUM orders extended from the WooCommerce orders and each of them has its own post type.:
1. Inventory Logs, with "atum_inventory_log"
2. Purchase Order, with "atum_purchase_order"
Hope this helps.
Best Regards,
José Andrés