The description in box 1a says "gross amount of payment card/third party network transactions", so if a sales tax is included, then it is part of the gross amount, so adjusting the amount as "too high" doesn't sound right.
I put the amount in "Enter business expenses not yet reported" and labeled it "Sales tax collected and reported on 1099-K". That's not great either, because it's not a business expense.
Maybe the guidance is somewhere on the TurboTax screens, but I didn't see it.
