Invoice number
The invoice number is the unique identifier of an invoice document; it must designate every document unmistakably and allow the link between document and entry to be checked.
Definition
It is widely assumed the number series must be gap-free. Swiss law does not expressly require that; what it requires is that the accounts be traceable. A gap is therefore not a breach, but it has to be explainable — and that becomes difficult precisely when nobody knows why it arose.
In practice a series tied to the year and carrying no internal meaning has proven itself: customer numbers or project codes inside the invoice number create conflicts as soon as the customer or project changes.
Where to read it
What the software must be able to do
Check whether the number is assigned automatically and never reused, whether several document series are possible — invoice, credit note, reversal — and whether assignment is logged. Manually assignable numbers are the most frequent cause of duplicate documents.
Checked Aug 2026
More terms under Invoicing, payment and banking: Advance payment Allowance for doubtful debts Bad debt camt.053 Cancellation invoice Cash discount Certificate of shortfall Credit note Creditor Current account Debt enforcement Debtor Default interest Delivery note Dunning eBill Final invoice IBAN ISO 20022 / camt Open items pain.001 Part payment Payment term Pro forma invoice QR reference QR-bill QR-IBAN Quotation Receipt Tips TWINT as a payment method Visitor taxes