Billing Switch Slot

Move one extra creator slot from one platform to another (body: {"from":"fansly","to":"onlyfans"}). Two item-quantity changes on the same Stripe subscription in one call; Stripe prorates each leg onto the next invoice, so you're billed (or credited) only the price difference between the two platforms' slot rates. Any connected but inactive creator on the destination platform that now fits is activated at once (optionally name one as creator_id).