Hello Aspirant! Yes you need to pay a seat acceptance fee of Rs.35000 after selecting the float option in JOSSA counselling process. If you get a seat in a particular college in the Josaa counselling and you're not satisfied with the branch then you may select the float option which means if your choice can be upgraded then it will or else you can continue with the current seat. And also, the seat acceptance fee will be added to the college fee. It's not the extra fee taken.
Hope this helps.