Make the costs explainable.

Separate shared platform allocation, client extras, usage and support estimates. A blank input is unknown, not a free service.

Decide who bears usage risk and how the client will understand charges before choosing a rebilling arrangement.

A rate is meaningful only when its unit, service, period and scope match the quantity you intend to estimate.

A client rebilling arrangement does not automatically remove the agency’s need to fund and reconcile upstream usage.

Estimate the work that keeps the client arrangement usable, then compare it with real observations after launch.

Record each add-on’s owner, renewal and cancellation evidence separately, even when it is marketed alongside the core plan.

Use explicit start, end and effective dates so a payment, usage total and service promise can be reconciled on the same basis.

Compare the same service, unit and period before concluding that a supplier cost or client collection is wrong.

Keep the old plan, proposed price and effective transition distinct; a new public price should not silently rewrite existing client expectations.