A sale price, an automatic promotion, and a customer discount code can each be correct by themselves. The risk is the final price they produce together.
Theme warnings are not a reliable safeguard. Checkout can be reached from several paths, and the price needs protection where Shopify evaluates the cart—not just on the product page.
I built HBN: Discount Floor Guard to enforce that boundary. Instead of trying to predict every possible discount combination, you set one minimum acceptable final price per rule. The rule can cover your whole catalog or narrow to specific products, variants, or collections. Country, customer tag, and B2B status let you create legitimate exceptions without weakening the policy for everyone else.
When a combination would push the price below the floor, the app blocks it in cart and checkout and shows the shopper a message you write—something practical like “This code cannot be combined with the current sale price. Remove the code or continue with the sale price.”
There is also a simulator so you can test the uncomfortable combinations before customers find them. Try a sale price plus a code plus an automatic offer, then add the country or customer tag that could change the outcome.
I should be upfront: this app enforces a minimum final price. It does not manage which discounts you offer or replace Shopify’s native discount engine. If what you need is a way to say “this product should never sell below $40 no matter which promotions apply,” that is what it does.
The free plan supports one active rule. Paid plans unlock additional rules and scoping. Full details are on the App Store listing.
I build this app, so take this as a developer suggestion. One question I would genuinely like feedback on: when you set a minimum price for a promotion, do you think in fixed dollar amounts, percentages off the regular price, or margin-based formulas? Which reference point is easiest for your team to maintain?
Official App Store listing: