As orders are printed on demand you shouldn't need to set inventory because they are "Unlimited Inventory"
However, if you see the shopify our of stock message, there are a couple of options you can look at to fix this.
1) un-ticking "tracking inventory"
2) select continue selling when out of stock" as described in this forum
https://community.shopify.com/c/technical-q-a/how-can-i-set-product-inventory-to-unlimited-in-shopify/td-p/1640309
3) set the inventory at a high level. Shopify have an Inventory tab but instead of it being built into each product it appears to only be for products that have inventory enabled as Inventory tracking is enabled at the variant level.
4) ensure shipping rates are set up for the Prodigi location
How can I fix the shopify out of stock message?
