[randomswede]

For digital downloads within the EU, the VAT rate depends on the location of the end customer (and must be paid to the tax office in the jurisdiction of that end customer).

Failing to do account for this at the time of sale creates legal and/or economic liabilities for your customer.

This means that the API between your platform and your customer would need to have (at least) "gross price", "VAT" and "jurisdiction" for each item, to allow for your customer to do proper book-keeping.