Every VAT invoice, including a self-billed one, needs a unique sequential number. In self-billing the customer assigns the number when they raise the invoice. Apex Billing gives each business its own sequence (for example SB-000123) and a separate sequence for credit notes (CN-000123), so numbering is continuous and auditable.
Key points
- Unique sequential numbers are a VAT requirement.
- The customer assigns the number when self-billing.
- Invoices and credit notes use separate sequences (SB- / CN-).
Why sequential numbering matters
A unique, unbroken sequence is a VAT requirement and makes invoices easy to audit — gaps or duplicates raise questions. Because the customer raises self-billed invoices, they own the sequence.
Separate credit-note numbering
Credit notes are numbered in their own series so they’re distinct from invoices while still sequential. Apex Billing keeps per-business SB- and CN- sequences automatically.
This is general information, not tax advice — confirm your own position with your accountant or HMRC (see VAT Notice 700/62 on self-billing).