Welcome back, comet52.

Thanks for keeping in touch and letting us know the results of the steps you've performed in trying to add sales tax using the GoPayment app.

I suggest reaching out to our Payments support. This issue requires a deeper investigation on why you're unable to add sales tax in a sale. Reach them by clicking the link and get the number under QuickBooks Online with Payments & Merchant Service Center.

If you have other questions about QuickBooks Payments, you may want to visit this page to find answers: QuickBooks Payments FAQ.

Reach us back if you have other concerns about working with payments. I'll be right here to help you. Take care!