Why do you list only the income accounts under Sales option while creating a plan and an addon?
A subscription business is considered to be a direct product/service selling business that involves customer paying to the merchant for the commodities he has asked for. Thus, the revenue coming to the merchant for the customer subscribing to his product/service should be taken in his income account only. Hence, only Income accounts are listed for the subscription plans/addons that are to be subscribed.
We’ve liability accounts listed for credit notes as the money for them can be acquired for different purposes and hence may serve as a liability for the merchant.