Assign multiple customers as a subcustomer?

You’ll need to manually assign each customer as a sub customer in your QuickBooks Online (QBO) account, @ewing-rj.

To achieve this, we’ll need to edit your customer’s information. I’d be glad to walk you through the steps.

1. Go to the Sales menu.
2. Select the Customers tab.
3. Locate and select your preferred customer.
4. Click Edit beside New transactions. 
5. Put a check in the Is sub-customer box.
6. Select a parent customer and click Save when done. 

For more details and additional insights in managing your customers, check out this link for reference: Add and manage customers in QuickBooks Online.

Furthermore, In case your customer overpays their invoice, you can utilize this link that can guide you on how to handle the situation: Handle a customer credit or overpayment in QuickBooks Online.

Know that I’m always around to back you up in case you have any other concerns or questions managing your customers. Just tag me in your reply and I’ll swing back into action. Keep safe and more success in your business!