#Purchasing Add-Ons

For a running Subscription, extra Add-Ons can be purchased that are compatible with the Subscription's underlying plan. Purchasing Add-Ons for custom subscriptions is not possible.

If a Subscription has Add-Ons associated with it, editing the Subscription is no longer supported.

When an Add-On is purchased, its contents are combined with the Subscription's existing items.

If a RateCard is present only in the Add-On, not in the Subscription, the RateCard is added to the Subscription as a new Item.
If a RateCard is already present in the Subscription, the existing item will be extended with the contents of the Add-On's RateCard.

The resulting items will keep the Subscription's alignment and billing cadence.

#Extendability

When an Add-On extends an existing Subscription Item, their properties are merged:

static prices are merged by summing them up.
boolean entitlements are merged into a single boolean entitlement.
metered entitlements are merged by summing their issueAfterReset if all other properties match.
usage discounts are concatenated as a list.

Combinations not listed above either have no effect or will result in validation errors during the compatibility checks. The list of compatible combinations will grow in time, but the default behavior of creating new Subscription Items already makes this a versatile toolkit: in general, we encourage breaking the contents of an Add-On into multiple RateCards.