Add more seats by paying less via PUT /v2/seats request manipulation

Summary: I could not fully test this vulnerability because the test plan must be completed for the payment process, that is, 30 days. But the price value in api also changes and if payment is made according to this value, wrong billing will occur.

seats = 5
amount = 300
bady.seats = 1.1

seats += Math.ceil(bady.seats)
// 5  +=             2
// seats : 7 

amount += Math.floor(bady.seats) * 60
// 300 +=                 1      * 60
// amount : 360