Hello there, @communityoil!
The Add function automatically posts the exact same transaction into your account register. You can utilize this if you haven't created a record of the same transaction in QuickBooks.
But if it's the opposite, you'll have to select Find Match instead to avoid creating a duplicate transaction. You can read through this article to learn more: Categorise and match online bank transactions in QuickBooks Online.
Lastly, here's a few articles you can read to help manage your customers and sales: Manage Customers and Income for QuickBooks Online.
Keep me posted in the comments if you have any other questions. I'll be here to lend a hand.
