we are offering SAAS where every user gets its own plan (because of flexible prices)
Now i have the possibility that a user has a Plan ID ABC123 with a fix price of 99 EUR and he decides to add a module, so the new price will be 129 EUR per month.
How should i go with that? Should i update only his Plan ID to the new price or must i change the subscription price? The new price is then valid for every month. So every upcoming billing should charge 129 EUR.
