You're correct. You can only process a full refund in the GoPayment app, HGA.

Alternatively, you can initiate the partial refund using the Reverse a Transaction feature from the Merchant Service Center page. I'll share the procedures below.

Here's how:

1. Log in to the Merchant Service Center.
2. Navigate to the Processing Tools menu and select Reverse a Transaction.
3. Enter the required details accordingly. Then, click Search.
   
4. Choose the appropriate transaction and manually input the refund value in the Amount field.
5. When the confirmation pop-up appears, pick Cancel to enter a partial refund amount.
6. Once done, hit Continue. After that, a receipt of the transaction will be displayed on the screen. You can either E-mail or Print a copy of the receipt.

Please know that the system only allows refund processing within six months from the date of the sale. Otherwise, you'll need to initiate the refund using cash or check. For more information, check out this link: Void or refund transactions in QuickBooks Payments.

Nevertheless, if the transaction is less than six months old and you still have no option to input a partial refund, it could be due to your limited user access. On the other hand, I recommend contacting our Customer Care Team if you're an Admin of the QuickBooks (QB) Payments account. They have the tools to help you resolve any payments-related concerns.

I'm also attaching this handful of resources you can review to maximize your experience when using the GoPayment app and QB Payments:
 

• Accept a cash payment in the GoPayments mobile app
• Download GoPayment sales tax report
• Common questions about QuickBooks Payments deposits in QuickBooks Online

You can always come back to this thread if you have follow-up queries about partial refund processing in QuickBooks. We'll be here at all times to assist you promptly.