Does invisalign payments count as a medical expense?

Yes, Invisalign expenses are dental expenses and can be deducted as Medical expenses.

Yes, the cost of orthodontic treatment is a legitimately deductible medical expense.    But remember that you may only deduct medical expenses that exceed 7.5% of your adjusted gross income - and you must itemize in order to do so.

But only the "principal" payments.  You cannot deduct any interest or fees.