accountId is your internal account ID/customer number for the corporate client.
parentAccountId is your internal account ID for the parent company of this account, assuming it has one and your app supports heirarchical customers.
billingAccountId is your internal account ID for the parent/grandparent company that this account is a decendant of, that has the billing relationship. (Assuming your app supports heirarchical customers).
paymentId and subscriptionId are the identifiers that link this specific accountId to your payment system (e.g. Stripe), that link to charges and subscriptions respectively.
Note: If this specific accountId is a child account, and the parentAccountId is linked to the payment system, only include the payment processor id's with the actual account that is linked.
metadata allows you to pass key-value pairs that might be useful in predicting or explaining behavior (industry, location, account tier etc)
