How to charge prorated rate on paypal subscription?

[anwarjut67]

Trying to set up a subscription via paypal rest API. I am looking on a solution on how to modify the subscription and charge the specific fee in 1 checkout. I found a way to change the quantity on the subscription, but the problem paypal does not prorate.

So for example, if user subscribes today with 10x of product and then changes the subscription to 20x of product, the paypal will not charge the prorated fee. So how to handle that?

This is an official msg from paypal: The new price is effective starting on the next billing cycle. Proration and one-time fees aren't automatically supported. If you want to prorate the difference at the time the plan changes or charge one-time fees, you need to do these manually. https://developer.paypal.com/docs/subscriptions/customize/revise-subscriptions/deepmaterialar

How do I charge it manually?

[Tilellimjx]

I asked tech support, and this was their response:

Thank you for contacting Merchant Technical Support. 

As described, proration is not supported. If you need to update pricing to adjust for this, please follow https://developer.paypal.com/docs/multiparty/subscriptions/customize/update-plan-pricing/ or https://developer.paypal.com/docs/api/subscriptions/v1/#plans_update-pricing-schemes. If you want to collect a single payment outside of this subscription, you can use invoicing. Thank you for your business and I hope you have a great day!

So invoicing is their solution to this problem. I looked at the documentation for invoicing and it looks like it could work, but there is going to be extra steps and won't be as elegant as PayPal supporting proration. 

Hope this helps.