Need help for Shopify Billing API

[Darakhsa Mansuri]

Hello Everyone,

I have make an app in Shopify with PHP MySQL technology as a backend,but now want to convert my free app into paid one. I need to use Recurring Billing Cycle for my app.
But unaware about how to use this billing api means i have several questions:

 1. where i have to trigger a call for charge ?
 2. how can i monitor payment history  for my app ? or I have to monitor payment history in DATABASE / is this will be showing up in Partner dashboard ?
 3. If i will use 30 day free trial then after apply recurring charges to shop owners then this thing will automatically managed by Shopify Billing API ?
 4. which payment gateway will be used by Shopify Billing API ?
 5. is there a way so that i will test this whole billing process on my shopify partner developer store [ Test Store ] ?
 6. One more question is : i have submit my app to shopify as a free app but currently its in review mode by shopify team [ Unpublished ], can I resubmit my app after i will achieve usage of billling API ?