One invoice per purchase rather than per order: a customer who buys a plan and
two add-ons in one go has bought once, and three invoices for one purchase is
three times the paperwork for the same money. Each order becomes a line, which
is also how the add-ons get listed individually.
Everything the document says is copied into the snapshot at the moment the
number is assigned — issuer, recipient, lines, rate, the reason for the rate.
A test changes the company name and the customer name afterwards and asserts
the invoice still says what it said. That is the whole reason no PDF is stored.
The number and the invoice commit in one transaction. A number taken and then
lost to a failure is a gap in a series that must not have one, and the refusal
test asserts that a rejected invoice leaves the counter where it was.
It refuses outright until the company details are complete. An invoice without
a registered name, an address or a VAT number is not a valid invoice here, and
issuing one consumes a number that can never be handed out again.
VAT comes from TaxTreatment, which already existed and already handles a
verified EU VAT ID correctly — including the reverse-charge note, without which
a zero-rated invoice says nothing about why no VAT was charged.
The billing address is carried as the lines it was written as. It is one
free-text field today, and guessing which line is the postcode would put it
where the street belongs, on a document nobody can correct afterwards.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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