metric	unit	population	definition	decision_use	guardrail_or_caveat
eligible_orders	orders	orders that passed product, order, inventory, market, and channel gates	Distinct original orders eligible for the campaign before assignment	Experiment denominator	Never use all store orders as the denominator.
offer_render_rate	percent	eligible orders assigned to treatment	Offers rendered successfully divided by eligible treatment orders	Diagnose channel or integration loss	Not a revenue outcome.
offer_accept_rate	percent	eligible treatment orders with a rendered offer	Customers selecting accept divided by rendered offers	Diagnose offer relevance and presentation	Acceptance is not proof that the order update, fulfillment, or contribution completed.
verified_add_on_rate	percent	all eligible treatment orders	Original orders with the exact offered variant successfully appended and paid divided by eligible treatment orders	Primary operational conversion	Reconcile accept events to order records and deduplicate retries.
net_add_on_revenue_per_eligible_order	USD per order	all eligible orders by assigned arm	Collected add-on revenue less add-on refunds divided by eligible orders	Compare treatment with holdout	Do not report gross accepted value as net revenue.
incremental_contribution_per_eligible_order	USD per order	all eligible orders by assigned arm	Net add-on revenue minus discount, COGS, incremental pick/pack, shipping, payment, app, support, return, and service costs; treatment minus holdout	Primary commercial decision metric	Requires a valid holdout or experiment; observational attribution is not causal.
offer_fulfillment_rate	percent	orders with a verified add-on	Add-on units fulfilled divided by verified appended add-on units	Detect inventory, hold, or operational failures	Segment split shipments and pickup orders.
offer_refund_or_return_rate	percent	matured verified add-on orders	Refunded or returned add-on units divided by matured fulfilled add-on units	Product-fit and margin guardrail	Use a fixed maturity window and reason codes.
wrong_product_support_rate	percent	matured verified add-on orders	Support contacts tagged wrong item, incompatibility, duplicate item, or unexpected charge divided by matured add-on orders	Trust and eligibility guardrail	Audit tagging quality before interpreting movement.
original_order_cancellation_rate	percent	all eligible orders by assigned arm	Original orders canceled within the defined window divided by eligible orders	Protect the first purchase	Compare treatment with holdout; investigate perceived pressure or order confusion.
email_unsubscribe_rate	percent	consented delivered cross-sell emails	Unique unsubscribes divided by delivered emails	Email pressure guardrail	Not applicable to the in-checkout post-purchase surface.
email_spam_complaint_rate	percent	consented delivered cross-sell emails	Unique spam complaints divided by delivered emails	Deliverability and consent guardrail	Stop or narrow the flow when policy or provider thresholds are approached.