Billing system where I control of WHEN and HOW MUCH to charge my customers

[ionu]

Hello!

I am looking to build a custom payment system where I am in full control of WHEN and HOW MUCH to charge my customers customers' Paypal accounts for. 

The reason for that is because I run a platform where the membership fee amount and recurrence are flexible depending on the services rendered to each specific customer. For that reason, I want to build an internal billing system that could charge my customers' respective Paypal accounts one-time transactions at any non-fixed date and for any non-fixed amount.

I understand that you can do that with Reference Transactions, but I dont want to use that path because Reference Transactions is not open to every Paypal account. I wouldnt want to give up on some of my customers or put them through unnecessary loops.

As an alternative, I believe that Billing Agreements ( https://developer.paypal.com/docs/api/payments.billing-agreements/v1/ ) would be the only way to go, but I dont know whether they offer all the flexibility described above: on-demand one-time charges, on-demand dates, on-demand amounts.

Can anyone confirm please, or how you would go about building this internal billing system?

Thank you very much in advance!