Usage invoices are still invoices. Tax authorities do not care that the quantity came from an API.
One tax line per rate
If two stubs share a tax rate, you may subtotal. If they do not, do not. A VAT line that cannot be traced to a stub is a future amendment.
Location is a fact on the book
The ship-to, bill-to, and seat location can disagree. The book names which one you use for tax. Scrip will not pick a default to look helpful.
Reverse charge
If reverse charge applies, print it as a stub with amount zero and a tax code. Silence is not reverse charge.
