Purchases domains, assigns mailboxes to them, and optionally exports those mailboxes to a third-party app — all in a single call. When you request mailboxes. You are only charged for the difference — the slots you still need. For example, if you request 10 mailboxes and already have 7 unused slots, you will only be charged for 3 additional slots.The slot plan type is derived automatically from your active plan — you do not need to pass it. Slot charges are included directly in the same Stripe invoice or checkout session as the domain purchase.