bmizerany1234

[woeful ruin]

Subscription Item can't be created before a Subscription is created. Subscription Item creation always requires a pre-created Subscription

[burnt crag]

.. and that subscription creates the items (e.g. si_123) without input from me?

[woeful ruin]

There are two possible ways to create Subscription Items:

1. Set items in Subscription that the Subscription Item will be created automatically: https://stripe.com/docs/api/subscriptions/create#create_subscription-items
2. Create Subscription Item manually after a Subscription is created: https://stripe.com/docs/api/subscription_items/create

Either way, you can re-use the Subscription Item to to update the existing Subscription or to schedule a future change with Subscription Schedule