Let me first welcome you here in the Community, thabosrmalema.
If you mean converting an invoice to a sales receipt, we're unable to perform this in QuickBooks Online. As a workaround, I suggest copying the information on the invoice. Then, let's create a sales receipt using the details.
Here's how to create a sales receipt:
Go to the + New icon.
Select Sales receipt.
Choose the name of the customer.
Enter all the sales information from the invoice.
Once done, click on Save and close.
Additionally, I've included an article that'll help you personalise your sales form in QuickBooks Online. This helps you add the information that matters most to your business: Customise Sales Forms.
I'm always here to provide assistance if you have other concerns. Feel free to reply here and I'll respond as soon as possible.
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