Hi SB115,

Processing batch file in QuickBooks Online is applicable for suppliers only. If you need to process or record customer credits due to an overpayment made, you can record an expense transaction to record the refund for your customer. Here's  how:

1. Click on the + New.
2. Click on Expense or Cheque.
3. Select the customer name you wanted to refund under Payee field.
4. Choose the Payment account where you deposited the overpayment.
5. In the Category column select Accounts Receivable account.
6. Enter amount and other fields, then click on Save and close.

Then, to link the refund and the overpayment click on Receive payment section. Here's how:

1. Click on the + New.
2. Click on Receive payment.
3. Select the customer name and then link the overpayment and the expense.
4. Click on Save and close.

You can check this link to learn more about how to Handle customer refunds in QuickBooks Online. 

Post again in the Community if you have further concerns.