I have a paper receipt book to give customers receipts. Can I upload these as invoices?

Thank you for reaching out, @regisappliance.

The option to import those paper receipts as invoices is unavailable. However, you can record it manually. Allow me to discuss this further.

You should only record an invoice if no payment has been made yet. However, if payment has already been received, you need to record it as a Sales Receipt.

Here's how:

1. Navigate to the + New, then select Sales receipt.
2. From the Customer ▼ dropdown, select the customer who made the payment. If you haven’t set up your customer yet, select + Add new.
3. From the Select a product/service ▼ dropdown, select the product or service that you sold.
4. Fill out the other necessary fields in the sales receipt, then select Save and Send.

Additionally, you can visit this article to import sales receipts via CSV: Create sales receipts in QuickBooks Online.

Moreover, I'll leave this article for you for your future use to explore how to reconcile your account in QBO: Reconcile an account in QuickBooks Online.

If you have further concerns, you can comment below.