Authorizes the registrar charge for a pending intent and creates the domain with
status: pending. Registration then continues asynchronously.

Requires an idempotency key, sent as the Idempotency-Key header or the idempotencyKey
body field. Retrying with the same key returns the same intent and domain without a second
charge. Rejections: 409 for expired, cancelled, failed, already-confirmed, unavailable, or
re-priced intents, 422 for a missing or reused key or a purchase above the organization
policy, 403 without the admin role or domains:purchase permission.