We have worked through the Taxamo API connection for both Plus and non-Plus stores across 4 our EU Plus stores. It’s pretty complex but doable if you have a good developer that supports Shopify. It’s kind of crazy that Taxamo chose to support Magento and not Shopify!
I might be able to provide the API configuration as service to other stores but I don’t see us going through a formal App process. Also, we could probably set up CBIT too but haven’t looked at it yet. Damon let me know if you want to chat about help with your API (you’ve chatted with several of my eCom friends this week but we were already deep into the Taxamo rabbit-hole!)
Kevin Williams