Voiding a posting, writing off a balance
Nothing is deleted. A mistake is reversed with a reason, and both lines stay visible.
Two different things, both needing a manager and both needing a reason.
Voiding reverses a posting that should not have been made — wrong folio, wrong amount, wrong head. The original line stays and a reversing line appears beside it. This is on purpose: a bill where charges quietly vanish is a bill nobody can audit, and the voids report is one of the first things a hotel's auditor asks for.
Writing off accepts that a balance will not be collected. It closes the folio without money arriving, with a reason, and it lands on the revenue journal as exactly that — not as a payment.
Both refuse with "a reason is required" if you skip it, and the reasons come from your hotel's own lists. If the reason you want is not offered, an administrator adds it in Lists & reasons — please do not pick the nearest wrong one, because that list is what the reports are grouped by.