We run stores for nonprofits who can't always afford to buy merch up front. They want to incorporate print-on-demand items like t-shirts, hats, bags, etc. to sell items and test new designs. The only option currently is an expensive custom API.
If we had to choose, Printify would be our choice because they have eco-friendly items and a larger selection than most. They have APIs set up for many e-commerce companies, but not Cart/AC.
We have lost stores/clients due to this limitation, and more are asking for this urgently. Please look into incorporating an API connection to at least one POD company.