The seat allottment will be done in 7 rounds for JOSAA Counselling. You can check the complete procedure at our page: https://engineering.careers360.com/articles/josaa-counselling . You need to make the payment only if you are allotted a seat. Let's say if you are not allotted a seat in the first round, you can try for a seat in the subsequent rounds when the seat allotment is done. But you have to make the payment only once you have been alotted a seat.