There may be instances where you invoice a client for a purchased service/package with the expectation that their insurance provider will cover the balance after the copayment is applied.
If the insurance provider decides to pay less than the balance due, you may need to record the difference as a write-off.
You can record a write-off for an invoice by going to your Billing & Payments page, then click Edit from the More Options menu (3 dots):
Select Record a write-off from the 3 dots in the top-right corner:
Add your write-off details in the popup, then click Add: