This thread suggests to me that complimentary subscriptions should show in Stripe as a pricing option.
Let me give a bit more context. My site will have a free newsletter and an optional paid membership that offers perks, so my members will be a mix of free and paid. I am offering an exclusive role in my Discord server for paid members, which is why I am building an integration.
Ghost offers webhooks for when a member is created, updated, or removed. New members are easy: if paid, proceed. Member Updated is not as useful because it triggers on every member update; when they login, when they change their email, etc. It may trigger dozens — eventually hundreds — of times a day. I only want to know when someone upgrades to paid or downgrades to free, so I thought it would be more efficient to simply track when new Stripe subscriptions are added or cancelled, and grant or remove the role accordingly.