If you're looking to automate your POD orders, I’d recommend checking out my company Demon (demondms.com). It integrates with your Squarespace store and IngramSpark so your customers can place orders, and Demon handles the print-on-demand ordering automatically—no need to manually fill orders.
It connects with your Squarespace using OAuth, then handles all of your print-on-demand order placement for you. It handles international orders (like selecting the printing region, and it even does the two factor automatically if you set it up to) and there's no limit to the number of orders.
There's good documentation, it ingests your products from IngramSpark automatically when you set up the integration, and for individual publishers with at most 10 POD products it's just $19.99 a month. It's not free, but it also takes away a lot of manual work. It also handles things that other systems don't, like placing POD orders across multiple different distributors.
IngramSpark has no API, and they haven't played ball with any integrations. I added this feature over the last year because of the closing of well-loved Small Press Distribution, which forced lots of small presses into tons of manual labor they couldn't afford to be doing. It does it by acting like a user - Demon has 3 dedicated servers that actually go out and do the work of placing the orders, getting the products, etc, 24/7. It is currently processing the orders for 3 medium-sized publishers every day.
Here's the documentation for Demon's IngramSpark and Squarespace integrations.
Demon is a tool primarily used by small- to medium-sized publishers, and it has been around for about 5 years now.
