This. Aren't there subtleties, for example, when doing inter-state commerce (assuming the two parties are both US-based)? In the EU, VAT isn't charged the same

This. Aren't there subtleties, for example, when doing inter-state commerce (assuming the two parties are both US-based)? In the EU, VAT isn't charged the same way if you invoice an entity based in your country or one based outside of it.