Headless eCommerce: Anyone have experience building an "API first" online shop?

Hi! I'm working on a proof of concept for an online shop. From early stage discussions it appears that the direction the UX is heading in won't fit the frontend model available via traditional eCommerce platforms such as Shopify, Magento, Bigcommerce etc.

For this reason I'm interested in an API based eCommerce platform, driven by an SPA frontend. Rather than reinvent the wheel, I've been investigating the current landscape, however, I suspect there may be solutions I am missing.

I've known about Moltin for some time and their platform looks promising. Unfortunately they seem to have gone down the route of obfuscating their pricing to the point of making it impossible to find out fees for their associated services without signing up first.

I've also had a look at Commerce.js (Chec), Storyblok and Ordercloud.io.

I'd be grateful for some general insight and advice from anyone with experience of using an API based/headless eCommerce solution, with particular regard to any pain points, pitfalls, and pleasant/not-so-pleasant surprises along the way!

Thanks for your help, hashnode.