How to Map PrestaShop Discount Collisions Before a Campaign

# How to Map PrestaShop Discount Collisions Before a Campaign A promotion can be correct in isolation and still produce the wrong commercial result. The difficult cases appear when a catalog price rule lowers a product before a cart rule checks its threshold, two cart rules share a priority, or compatibility settings exclude an offer the campaign team expects to stack. Start with the interaction surface, not a list of discounts. For every active rule, record its time window, shop, currency, country, customer group, carrier, product scope, minimum threshold, reduction type, and priority. Two rules deserve attention when their windows overlap and every constrained dimension has at least one shared value. Broad dimensions count as potential overlap, not proof of safety. Next, separate the evaluation stages. Catalog price rules affect product pricing before cart rules are ordered. That means a modest catalog reduction followed by two percentage cart rules can create a much larger effective reduction than any campaign brief names. Sequential percentages compound: 20% followed by 30% removes 44%, not 50%, but the margin consequence can still be severe. Compatibility deserves its own check. If a cart rule restricts combinations, an overlapping rule not present in its allowed set can be blocked. Priority then becomes an outcome control. Equal priorities introduce an ID-order tie-breaker that is stable but rarely obvious to campaign operators. [Vamao PrestaShop Discount Collision OS](/products/vamao-prestashop-discount-collision-os) builds this map read-only and replays a representative scope without editing merchant promotions. Use it as a preflight layer, then validate important carts in a disposable storefront before launch.