Thanks for posting here, @tarabrown.

To help you match your downloaded sales receipt to an existing transaction in QuickBooks Online (QBO). Here are the steps you can perform:

1. Navigate to the Banking/Transactions menu.
2. Click the tile for the account you want to review.
3. Select the For Review tab.
4. Look for the sales receipt and click it to expand the view.
5. Select the Find Match option.
6. From the Match transactions page, review the records found in QuickBooks. This is the possible matching transaction you already entered in QuickBooks.
7. Make sure this is the correct match. Check the Deposit to, Payment method, and Bank account fields on forms for the existing transaction in QuickBooks.
8. If this is the correct match, select Save.

For more info about this, please visit this article: Categorize and match online bank transactions in QuickBooks Online.

In case you're now ready to reconcile your transactions to guarantee that your bank balance and QBO are matched, check out this article for the detailed steps: Reconcile an account in QuickBooks Online. 

If you need more help about matching your sales receipt in QBO, you can always get back to this thread. Take care always.