I think, you refer to business customers b2b in your posting, because private customers do not have a tax ID. If businesses have to pay value added taxes VAT (very small businesses are excluded from VAT in almost every European country), then either the end customer has to pay it, or the business receiving the VAT invoice can claim a deduction from the VAT they owe to the tax office from their own VAT sales. VAT rates vary a lot between European countries and countries on other continents may have a completely different taxation system. That's why we are using payment services like Stripe or PayPal. They offer a system (e.g. Stripe Tax) that can handle sales from a business in one country to a customer (private or business) in another country. Certainly, they will take an additional provision for that.
What it will need to integrate Stripe Tax service to work with UNA is a handler in the API call, that is called automatic_tax[enabled]"=true , which will trigger VAT handling as is set up in Stripe Tax.
This information is from this site https://stripe.com/at/tax (I don't know how to change to the english version of the page, sorry).