Nice to have you in the Community space, @nickng.
To attach receipts from the Banking tab, you’ll want to ensure the receipt is already added in the Reviewed tab. That way, you can attach it to your transactions.
If you’re attaching it to an imported bank transactions, ensure that the receipts and the transactions are already added in QuickBooks. This way, you'll be able to match the receipts with an existing record in QuickBooks. To learn more about attaching receipts in QuickBooks Online (QBO), you can read through this article for reference: Capture and categorise receipts and bills.
I also have here an article that you can read and can guide you through the steps on how to email receipts to your QBO account.
Let me know if there’s anything else you need help with attaching receipts in your QBO account. It’s always my pleasure to help you. Have a great day and keep safe.
