Refill
Refill is delivery a panel repeats, at no extra charge, to restore a count that dropped after an order completed, within the window and conditions the service terms set.
A refill has three parts, and a service that does not state all three leaves the decision to the panel at the moment you ask. The window is how long you can still claim, counted from the order date, from delivery starting or from completion, depending on the terms. The trigger is what has to happen before a claim is accepted, usually a fall below a certain level. The scope is which orders qualify: some panels exclude partial orders, orders whose link changed, or accounts that were renamed or made private.
The check is arithmetic, and the usual baseline is the start count plus the quantity ordered. The panel takes the start count recorded when delivery began, adds the quantity you ordered, and compares the result with the current count. A few panels ask only that the count fall below the quantity ordered, so the service terms are worth reading for which of the two applies. If you order 1,000 followers at a start count of 5,000 and the account now shows 5,700, the panel sees a shortfall of 300 and refills up to that. If the account also gained 400 followers organically in the meantime, it shows 6,100 against a target of 6,000 and the claim is refused, even though 300 delivered followers have left.
Refill is requested through a refill button on the order or through a support ticket, and a panel that resells passes the request upstream. It can only refill if its own supplier still honours refill on that service. When the supplier withdraws the service, the refill you were promised can disappear with it, so a long refill window from a reseller is only as dependable as the chain behind it.
Why a refill returns no money
A buyer who reads refill as insurance is reading too much into it: the count can still fall. It means some of what falls may be replaced, on request, within the window. It is not a refund either: a refill puts engagement back and returns no money, and a service with a refill button can still refuse a claim that falls outside the written trigger or scope.