A sent invoice is wrong

A sent invoice is locked, so it stays as the client received it. To put it right:

1. Open the invoice.
2. Click More, beside PDF.
3. Click Unlock to change it. It goes back to a draft.
4. Correct the estimate if the mistake came from there, then click Update from the estimate on the invoice. Or change the invoice lines yourself.
5. Send it again.

It keeps the same number. If the invoice should not have gone at all, click More, then Void, instead.