What an add-on is, and isn’t
An add-on is scoped work with a defined deliverable and an end state. A tier is capacity held open continuously. Paid once, an add-on carries no commitment and may be purchased again. Paid monthly, it is a 12-month term at the lower rate, and that commitment exists only because you chose it.
An add-on is never a missing piece of a plan. A plan moves your business forward from today; an add-on repairs something that was already broken behind it. Paid once, the job is complete when the deliverable lands, buy it again whenever it is needed, with no commitment in between. Paid monthly, the same work continues month after month for a 12-month term at a lower rate; that term is the one commitment an add-on ever carries, and it is there because you chose it. If what you actually need is ongoing publishing and growth, we will say so and point you at the plans instead of selling you the wrong thing.