I am trying to match a transaction butget a message saying it is already matched with another downloadedtransaction. How do I sort this out?

I know how to sort matched transactions in QuickBooks Online (QBO), userchris6. 

When you encounter a message stating that a transaction is already matched with another downloaded transaction, it means that QuickBooks has identified a duplicate transaction.

To sort this out, we can look for the transactions marked as matched. If you find that QuickBooks has incorrectly matched a transaction, you can unmatch it.

1. Navigate to Transactions, then select Bank Transactions.
2. Select the tile for the bank or credit card account you downloaded the transaction from.
3. Click the Categorized tab.
4. Locate the transaction you wish to unmatch.
5. Select the blue transaction link in the Added or Matched column to see the matched transaction.
6. From the Action column, click Undo.

Once done, you can manually match it with the correct transaction from your bank feed. You can read through this article for more detailed information: Match online bank transactions in QuickBooks Online.

Additionally, these articles may be helpful to you if you intend to reconcile your account:

• Reconcile an account in QuickBooks Online
• Learn the reconcile workflow in QuickBooks

This thread is still open if you have more questions about matching bank transactions in QBO. We'll be glad to help you out.