Where do I add the mortgage payoff amount for sale of my personal residence? It's not included under the "Sales Expenses" on the TurboTax page

This is posted to the area that was when you still owned the home.

Log into TurboTax

1. Choose Deductions & Credits
2. Scroll to Your Home
3. Select Mortgage Interest and Refinancing (Form 1098)

The payoff of a home mortgage is not entered on a tax return.  Nor is it used in the calculation of the gain or loss on the home sale.