QBO tries to match a regularly occurring transaction of the same dollar amount. How do I tell it that the transaction is new and should NOT be matched?

I can assist you in determining whether the transaction is new or old so that you can match accurately, 23072. This way, your books will stay accurate at all times.

You can tell that the transaction is new and should not be matched by looking at the Date. I recommend clicking the Find other matches button in the Banking tab to review the transactions. See the sample screenshot below for reference:

In addition, the transactions will match automatically if the payees, date, and the amount is the same. If you want, you can add Memo to the sales forms to quickly identify. 

For more details, see this article: Categorize and match online bank transactions in QuickBooks Online.

If you have spare time, you can read the following articles below to learn how to use bank rules to categorize transactions from your bank automatically and reconcile them: 

• Set up bank rules to categorize online banking transactions in QuickBooks Online.
• Reconcile an account in QuickBooks Online.

It was an absolute pleasure helping you today. Feel free to reach out if you ever need assistance in the future about managing your vendor transactions. Keep safe always, @23072-aamcocente.