Implementing vacant seats logic for Stripe with Pay

[ogirginc]

On our app, we want to charge per seat per user for the billing period. This logic is nearly implemented, except for this scenario below:

1. A company has started a yearly subscription for 3 seats (quantity) on 1st January 2025.
2. In March, one user has left the company. We now have 2 users but 3 seats for the remaining billing period.
3. In June, a new user has joined, and should fill the vacant seat.
4. On 1st January 2026 (after a year passed), when the billing period ends, we need to charge for only 3 seats.

Before this scenario came up, we had naively implemented by updating the quantity of current subscription like below:

current_subscription.change_quantity(team.users_count, proration_behavior: 'none')

However, if we follow this logic, the second step will reduce the quantity of current subscription to 2, and in the third step, we will charge the customer again, even though there are actually be 3 seats.

From what I read in the Stripe docs, it seems the Stripey way to implement such a feature is by using Stripe's Subscription schedules API.

As this API is not covered by pay gem, I am wondering if anyone has ever implemented such a feature using pay + Stripe gems? Or do you have any suggestions regarding this feature?

Here is the example of increasing quantity via scheduling API: https://docs.stripe.com/billing/subscriptions/subscription-schedules/use-cases#increasing-quantity

[excid3]

You can use the Stripe API directly for those pieces that Pay doesn't handle.