hi Comet, if you already have QuickBooks Payments and QBO, then using GoPayment is a good solution. It's a free app, made by Intuit, there are versions for iOS and Android phones / tablets.  There is no subscription fee for the app.  If you log in with your QBO login, the app connects to your QBO account.

If you are only making a few sales, you can use just the GoPayment app to enter customers' card info manually.  The transaction fee is higher than if you took the card electronically.  You'll probably want to enter these as New Sales on GoPayment (unless you want to track and edit a lot of customer info on these, in which case you'd want to create a Quick Invoice).

The transaction on GoPayment will automatically be created in your QBO account -New Sales on GoPayment create Sales Receipts in QBO.  Quick Invoice on GoPayment -> Invoice, editable in QBO.

QuickBooks has a blue tooth card reader that pairs with the app, you can order it from inside the GoPayment app.  The fees for the card transactions are lower than for manually entering the card number, so depending on the value of the transactions or the volume, it might quickly make sense to buy the card reader.