What are base plans and offers on Google Play?

A subscription can have several base plans, for example a monthly auto-renewing plan, a yearly auto-renewing plan and a monthly prepaid plan. Each subscription can hold up to 250 base plans and offers in total, with at most 50 active at once. A base plan can be bought without an offer. An offer is only available to customers who meet its eligibility rule: new customer acquisition, an upgrade from another plan, or a rule that you check yourself in your app (a developer-determined offer).

An offer has one or more phases. A free trial phase can last from 3 days to 3 years. An introductory price phase can be one payment or up to 52 recurring payments at a lower price. After the last phase the subscription renews at the base plan price. In the billing flow, your app picks the base plan or offer through its offer token.

RevenueDot stores a Google Play subscription as subscriptionId:basePlanId, for example pro:monthly. It records each period's offer id and an offer type of free_trial, introductory or unspecified, and it sends the offer id as offer_code in webhooks.

Sources: Play Console Help: Understanding subscriptions · Play Console Help: Create and manage subscriptions · Android Developers: Subscriptions