Our use case is that the customer will initially select a plan and then he would be charged for it only on 1st of every month. Can you clarify on this whether it is post or pre payment?

Say the customer selects a plan on 3rd Aug 2018 and cancels it on 23rd Aug 2018, then we want to bill him only for those 20 days and that too only on 1st Sept 2018. That being said, we want the customer to verify their credit card (if possible without charging him or using a token amount which should be refunded) while selecting the plan so that we can auto collect the amount.

I couldn't find anything regarding the token amount in the documentation. We are using the customer, product, plan, subscription and hostedpages APIs till now.