Apply to a Bill
Applying a credit reduces what you owe and therefore what you send.
It is reversible, it moves no money, and it is the step people skip immediately before overpaying a supplier.

Apply it
Open the bill, or the credit
Both offer the same action. From the bill, available credits are listed; from the credit, open bills are.
Choose how much to apply
Up to the bill balance or the credit remaining, whichever is smaller.
Save
The bill balance drops. A bill reaching zero moves to Paid.
- A credit can be spread across several bills until it is used up.
- It can be applied to bills dated after it, not only to the original.
- Applying can be undone. Remove the allocation and the credit is available again.
- Credits can also be applied during payment allocation, which is where a payment run picks them up.
Unused credits at period end
An unapplied vendor credit reduces what you owe without showing against any particular bill, so your payables can read as higher than the supplier believes. Apply credits before every payment run, and again before you close a period.