Tax
Tax is the intersection of who and what. The same pump is 19% to a German customer, 0% with a reverse-charge notice to a French business, and outside scope to a customer in Norway. A rate stored on the part cannot express any of those; a rate stored on the customer cannot express that the same customer buys both books and machines. So the liability hangs off the party, the category off the part, and the matrix joins them.
Tax authorities
The body that levies it, and the number the company is registered under with them — a company selling into three member states holds three registrations and must print the right one on each invoice.
Tax categories
What is being sold — standard, reduced, zero-rated. Lives on the part.
Tax liabilities
Who is being billed, and their situation. Reverse charge is a flag rather than a zero rate because an EU B2B sale charges nothing and is still reported: the taxable amount goes on the return, the buyer self-accounts, and the invoice has to say so. A zero rate loses all three.
Taxes and rates
A rate is effective from a date, never edited in place. Germany moved 19% to 16% and back inside seven months in 2020, and an invoice raised in that window has to reprint with the rate it was raised at. A rate naming a category beats the catch-all.
Which taxes apply to which liability
The matrix. Print order matters: an invoice whose tax lines move between two prints of the same document is one nobody can reconcile against the copy they were sent.
Check a calculation
The only question anybody asks afterwards is “why is this invoice 190.00”. This names the rate, the date it took effect, and whether it came from the category or the fallback.
Tax report categories
The section of the form a box belongs to — turnover, then input tax, then the payable. Order is part of the form, not a display preference: a return whose boxes move between two runs is one nobody can check against the paper.
Tax boxes
The literal number on the form — German UStVA 81, 66, 83. DSS4 never invents these; an operator copies them off the tax office’s own paper.
Which taxes feed which box
Point a box at a tax, on one side of the return, by one figure, with a sign. Re-adding the same combination corrects it — there is no separate edit.
Reverse-charged and exempt amounts only exist on the output side — a supplier’s invoice has no such breakdown, so input tax only ever offers the taxable amount or the tax itself.
Input tax is usually subtracted — without a sign the payable comes out wrong by twice the input tax, and the number still looks plausible.
Once a box has its sources, check the figures on the Tax Return.