Coupon Stacking

Coupon stacking is the close cousin of discount stacking, with the specific connotation of multiple human-facing coupon codes (rather than automatic discounts) being combined on one order. The pattern matters because most checkout systems treat coupon codes as independently valid: each code's logic checks whether the customer is eligible and the cart qualifies, but few systems check the cumulative effect of two or three codes against margin policy. The result is that a customer who legitimately has a welcome code, a loyalty code, and a referrer code can stack all three on a $50 order, taking $20 off, and the checkout flow treats this as the customer simply 'using their codes well,' even though the resulting margin is negative once fulfillment cost and payment processing are netted out. Native Shopify since early 2023 supports a 'cannot be combined' flag per discount, which addresses simple cases, but: (1) the flag is per-discount and must be configured manually for every new promo; (2) it does not understand margin, only blocking technical combination rather than below-floor combination; (3) it interacts unpredictably with automatic discounts, app-based promos, and Shopify Plus Function-based discounts. A robust approach works at two points. Inside checkout, combination settings and discount Functions decide which codes may apply together; a best-offer-wins rule, keeping only the customer's highest-value code, is a common design. After the order is placed, a per-order margin check inspects the full discount stack (regardless of source), calculates margin with live COGS, freight, fees, and FX, and flags the order or holds it before fulfillment if the stack landed below floor. This is the approach Agentis takes: it does not change the cart, but it makes sure a below-floor stack does not ship unreviewed, and its records show which combinations keep breaching so the checkout settings can be tightened. The coupon-stacking conversation is also a customer-experience conversation: aggressively rejecting stacks in checkout is a conversion risk, while letting reasonable stacks through and catching the few that cannot be afforded before they ship protects margin without adding friction for most customers.