A timestamp alone said "some number was checked once": editing the field left
it intact, so a customer could swap a verified foreign VAT ID for any
plausible-looking one and keep zero-VAT pricing. The verified value is stored
and compared, which makes the rule self-enforcing — no writer has to remember
to clear a flag, and there are several writers.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Any non-empty string starting with two characters other than AT switched the
customer to reverse charge — typing "XX123" was a 20 % discount. Reverse charge
now requires a VAT ID that is verified, belongs to an EU member state other than
ours, and looks like a VAT number at all. Unverified is the normal state and
means the domestic rate: over-collecting is correctable, under-collecting is a
tax liability.
Changing the number clears its verification. Verification itself (VIES) is not
built yet, so reverse charge stays off until someone confirms a number — which
is the safe direction to be wrong in.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Codex was right that this could misstate real charges: an EU business with a
VAT ID registered in another country is billed under reverse charge, and we
were adding 20 % Austrian VAT to their total anyway. TaxTreatment resolves it
from the customer's VAT ID, and the whole page — cart, plan cards, add-on
cards — now states one treatment instead of contradicting itself.
Explicitly NOT handled: cross-border sales to private individuals, which are
taxed at the buyer's national rate under OSS. That needs a maintained rate
table and a tax adviser, not a guess, so those fall back to the domestic rate —
over-collecting rather than under-collecting.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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