You have to pay for each attempt. However, there are multiple-cycle packages that provide a discount but if you get pregnant the first try, you do not get any money back. It's like insurance- you pay but may not need it. There are also refund packages that may cost more but if it doesn't work you get a percentage back.
Even with previous failed cycles, if you put back 3, they can all take. It is very risky. I know a cycled that cycled 9 times and ended up with twins.

