This can be either the customer's primary domain name or the customer's unique identifier. If the domain name for a customer changes, the old domain name cannot be used to access the customer, but the customer's unique identifier (as returned by the API) can always be used. We recommend storing the unique identifier in your systems where applicable.

This is a required property. The subscriptionId is the subscription identifier and is unique for each customer. Since a subscriptionId changes when a subscription is updated, we recommend to not use this ID as a key for persistent data. And the subscriptionId can be found using the retrieve all reseller subscriptions method.