I appreciate your detailed explanation of the invoice, Steve. The option to attach multiple invoices to one payment isn't available in QuickBooks Self-Employed (QBSE).
Once you receive the customer payment, you can only mark the invoice as paid. Please note that the Receive Payment option is not supported in QBSE.
Here's how to mark the invoice as paid:
- Go to Invoices.
- Locate the invoice.
- Under the Action column, click Mark as paid.

Once the payment is downloaded, you can categorise your transactions to organize your financial data.
You can always circle back to this thread if you have additional queries regarding invoices or other QuickBooks-related concerns. The Community is available to assist you 24/7.