Has anyone used Carvana to take over their lease or to buy their leased car? How does it work with sales tax in DC?

We have more value left in our leased car than the price at the dealership. So Carvana is offering $3500 more for our leased car.

Would we have to buy the car and then sell to Carvana? And if so, what happens with taxes in DC?

Or does carvana simply take over your lease and pay you the difference?