Need few people to signup somewhere as free trial
Will pay $1.5 each
payment: BTC
credit card/PayPal required but you won't be charged
you can cancel before the free trial expires
First you need to explain the whole process so that people can understand the task.
Second you should put the funds on escrow to give a assurance that people who will sign up can get the amount what you promised.
Also hopefully you are doing any illegal since for sure it will give you a bad impression here and might get a red trust if that really is.