An invoice or a bill is the most common kind of document in your books, and it's also the one most people have the clearest intuition for what "shouldn't be allowed" — you know, without being told, that quietly changing an invoice after you've sent it to a customer feels wrong. That intuition is exactly the rule the ledger enforces.
Draft, then issued — one meaningful transition
A document starts as a draft: fully editable, no number assigned, not yet a real thing your customer or supplier has a copy of. Issuing it is the deliberate step that changes that — it's allocated the next number in your sequence, its content is fixed, and from that point it behaves the way the physical or PDF document it represents behaves: something that exists, that someone else has a copy of, and that you can't retroactively rewrite.
That's a narrower window for editing than some tools allow, and it's narrower on purpose. Once your customer has an invoice number and an amount, your books and their expectation of what they owe have to agree — an editable "issued" invoice is really just a draft that a customer happens to have already seen.
Numbering is sequential for a reason
Invoice and credit note numbers are allocated in order at the moment of issuing, never reused and never assignable by hand. That gapless sequence isn't a cosmetic detail — it's evidence. A numbering run with no gaps tells anyone reviewing your books (an accountant, an auditor, HMRC) that nothing has been quietly issued and then removed. A gap, or a number that was reused, is exactly the kind of thing a reviewer is trained to notice and ask about.
Correcting an issued document: credit note, not delete
Mistakes happen — wrong amount, wrong customer, a line that shouldn't have been on there. The correct fix for an issued invoice isn't deleting it; it's a credit note, which reduces or fully cancels the original while remaining visible in the numbering sequence and in your customer's records. A credit note is the accounting equivalent of the reversal principle described in the Ideal Ledger's core rules: the mistake and its correction both stay on the record, rather than one silently erasing the other.
The same logic applies to bills from your suppliers. A bill goes through the same draft-then-committed lifecycle, and once it's recorded, correcting it means a credit or an adjustment against it — not editing the original figure your supplier actually charged you.
Why a document being paid doesn't change any of this
Whether or not an invoice has been paid, its issued content stays fixed. This matters specifically because payment status and document content are two separate facts: how much you invoiced for is one question, and how much has actually been settled against it is another (covered in Bank & payments). Keeping them separate means a payment being applied, part-applied, or reversed never has to reach back and change what the original invoice said — it only ever changes what's recorded as paid against it.
Why the moment of issuing is the one that counts
It's tempting to think of "sent" as the meaningful line — the point where an invoice becomes real. In practice, issuing (which assigns the number and locks the content) is what matters, and it happens before you actually send anything to your customer. That ordering is deliberate: the document is committed and numbered first, so there's never a state where a customer has a copy of an invoice that doesn't yet formally exist in your own books, or where you could issue two different versions of "invoice #1042" depending on who's asking.
It also means a document you've issued but haven't yet emailed or handed over is still treated with the same care as one your customer already has — because from the moment it's issued, it's occupying a number in your sequence and standing as a fact in your books, whether or not it's physically reached anyone yet.
What this looks like day to day
You can draft, edit and redraft an invoice as many times as you like before you send it. The moment you issue it, the ledger treats it the way your customer will — as a fixed, numbered document. If something's wrong after that point, you'll reach for a credit note rather than an edit box, and both the original and the correction will still be there for anyone — including future you — checking what actually happened.