A broken discount code turns shoppers away. An over-generous one bleeds margin. Both fail silently, no warning. PromoProof builds a real cart and checks each discount exactly the way Shopify does, confirming it applies and matches the amount you set, to the cent. Catch a ghost discount before a customer does, or stacking rules that quietly over-discount. No theme code, no scripts added to your storefront. It only alerts after re-confirming a real problem, so every email is worth acting on.

• Catches ghost discounts: codes that look live but silently stop applying
• Catches stacking conflicts that quietly over-discount and eat margin
• Alerts by email or Slack the moment a problem is confirmed