It depends on what happened:
They paid you outside Streamlined: record it as an external payment.
The amount is wrong: record a credit note or debit note.
They shouldn't pay what's left: void the invoice.
You're sending money back: issue a refund.
Money arrived outside Streamlined
For cash, or a check deposited at your own bank, record an external payment. The invoice balance drops right away. See record a payment you received outside Streamlined.
Money that came through Streamlined
Don't record card and bank debit payments, bank transfers to the details on your invoices, or checks mailed to your lockbox. They show up on their own. Recording them too counts the money twice. If one is waiting to be matched, match it to an invoice.
Lower the balance for a discount, deduction, or write-off
Record a credit note. It lowers what's owed on one invoice and moves no money. If a balance is left, your customer is usually emailed that it changed. A credit note that brings the balance to zero sends nothing. See credit notes and debit notes.
Raise the balance for an extra charge
Record a debit note. It adds to what's owed on one invoice. Your customer is usually emailed that their balance changed.
Cancel everything still owed
Void the invoice. The remaining balance drops to zero, and payments already made stay. If your customer's billing address has an email, they're emailed that it was voided. See void an invoice.
Note: Voiding is permanent. A voided invoice can't be reopened. If you void the wrong one, duplicate it and issue the copy.
Send money back to your customer
Issue a refund. It returns all or part of a card, bank debit, bank transfer, or check payment once the money has cleared. The amount goes back on the invoice balance, so a paid invoice opens again. Payments you recorded yourself and Shopify payments can't be refunded in Streamlined. See refund a payment.
Note: A refund is final once issued, and each payment can be refunded only once.
Who can use this feature?
Team members with Transactions and Invoices access, for payments, notes, and refunds
Team members with Invoices access, to void an invoice
Available on all plans