I've accidentally clicked the "Post" button - unknown transaction - can I undo this?

Yes, Peter. We can easily undo a transaction you accidentally posted in QuickBooks Online (QBO). Allow me to assist you further.

If it was a downloaded bank transaction that you categorized and added from the Accounting tab, follow the steps below:

1. Select Bank transaction.
2. Click Posted, then filter the date to find the transaction you accidentally posted.
3. Locate that transaction and in the Action column, hit Undo.

The transaction will then move back to the Pending tab, and the accounts will be adjusted to remove the posting.

If you meant something else, please feel free to leave a post below.

But, I don't know what transaction got mistakenly posted.  It was an accident - I accidentally clicked Post on a transaction but because the transaction disappears as soon as you click Post I never saw what transaction it was. 

To identify the transaction you mistakenly posted, we can utilize the Audit Log feature in QuickBooks Online (QBO), Peter.

Here's how:

1. Log in to your QBO account.
2. Go to the Gear icon and select Audit log.
   
   
3. Use the fields on the page to choose the appropriate User, Date, or Events filter to narrow the results.
   
   

Once identified, you can follow the steps of my colleague above to undo the transaction.

For more information on using the Audit log, you can check out this article: Use the audit log in QuickBooks Online.

Please feel free to respond below with updates on how things are progressing on your end.