I currently allow subscriptions via Paypal and Google Wallet. I'm looking for additional functionality that will allow me to modify the amount of (or add to) subscription payment per user's usage.
For example: if user subscribed to $5 a month plan and decides to buy additional feature for $2, I need a way to add that $2 to current $5 subscription amount as an one-off payment.
There is already a solution like that with Stripe Metered Payments I'm curious if I can accomplish same with Paypal and GoogleWallet.
It looks like this could be done with:
Paypal Adaptive Payments by pre-approving payments
Merchant Handled subscriptions for Google Wallet.