A purchase-able entity for a subscription product.
For Google subscriptions: If this SubscriptionOption represents a base plan, this will be the basePlanId. If it represents an offer, it will be {basePlanId}:{offerId}
True if this SubscriptionOption represents a Google subscription base plan (rather than an offer). Not applicable for Amazon subscriptions.
Pricing phases defining a user's payment plan for the product over time.
Tags defined on the base plan or offer. Empty for Amazon.