Thank you for the screenshot you've added, @twin Island.

I'm here to help you with recording a partial refund to your customer.

Since your customer wants to cancel the service, you can delete or void the invoice. Once the invoice is deleted, record the $100 advance payment as a deposit to Accounts Receivable. Here's how:

1. Go to the +New icon, then click on Bank Deposit under Other.
2. Select the customer's name, then choose Accounts Receivable (A/R) under the Account column.
3. Enter the amount, then save the transaction.

From there, the customer will have -$100 balance from his/her profile.

To issue a refund, create a check to AR, then add the $25 deduction as a negative amount (charge or fees).

1. Go to the +New icon, then select Check.
2. Add the customer's name under the Payee section.
3. Fill in the information, then pick the AR and expense accounts under the Category column.
4. Input the amount, then save the transaction.

Once you go back to the customer's transaction list, the balance will now show as $0.00 with no overdue amounts.

For more tips about handling customer refund in QuickBooks Online, you can open this link: Record a customer refund in QuickBooks Online.

Moreover, you can review the topics from this article for more hints about handling sales and customer transactions in the future: Topics about your company's income and customers.

If you have any other follow-up questions about handling refunds, please let me know by adding a comment below. I'm always here to help. Have a good one!