Why a paid + completed invoice locks

A paid invoice locks. Once an invoice reaches Paid, GM stops accepting edits or status changes — the only way out is an explicit cancellation with a reason. This is deliberate: a paid invoice is a financial record, and silently editing it after the money changed hands is exactly what you don’t want.

What locking means

Line items, amounts, and status are frozen on a paid invoice.
The status-change buttons disappear and a green “Invoice paid — no further changes allowed” notice shows instead.
Re-running a payment confirmation on an already-paid invoice does nothing and never resends the receipt.

Marking a completed service paid won’t un-pay it.Updating the service progress on a job that’s already paid used to be able to knock the invoice back to issued — that’s fixed. A paid invoice stays paid regardless of what happens to the service status afterwards.

Cancelling a paid invoice

Cancelling an invoice that has already been paid is treated as a refund/dispute, so GM requires an audit trail:

You must enter a non-empty note explaining why — the form won’t submit without it.
The warning makes clear that funds were already collected and any refund must be processed manually (GM does not auto-refund).
The cancellation and your note are recorded.

Cancellation is also terminal. See Mark an invoice as paid for how invoices get to Paid in the first place.