Is there a way to refund a customer to their original payment method? I don't have a register I just use quickbooks online.

Yes, geckosmart. There's a way to process a refund in QuickBooks (QB) Online.

For the fund that was transferred via ACH, you can record the refund manually in QBO as a Refund receipt:

1. Go to the + New menu and choose Refund receipt.
2. Pick the appropriate Customer and input the Refund Receipt Date.
3. Enter the original sale's full details.
   1. To issue a refund to the customer's Credit Card (CC), select Credit Card as the Payment method and enter the credit card details of your customer.
      
   2. If this money should transferred back to their bank account, the Payment Method should be Direct Debit.
4. Choose the account you've used to refund your customer in the Refund From field.
5. Double-check everything, and once done, hit Save and close.

If the customer paid you via CC, you can process the refund by opening the sales transaction (sales receipt or invoice payment) directly from the All sales window:

1. Go to the Sales menu.
2. Navigate to the All sales tab.
3. Modify the transaction Type, Date, and Customer fields accordingly.
4. Click View/Edit under the Action column.
5. Tick the More option and select Refund.
   

    

To gather more insights about customer refunds in QuickBooks, review this link: Void or refund customer payments.

You may also optimize your accounting management in the platform with the help of our QuickBooks Live Expert Assisted team. They can assist you with your bookkeeping needs so you can maximize your business operations.

By the end of the month, you can notify your customers about their outstanding balances that they need to settle by sending a customer statement. For more details, explore this article: Create and send customer statements in QuickBooks Online.

You're always welcome to this thread if you need more help with your QuickBooks needs.