“I have a code for the wax, but nothing more comes off.”
An item gets one product discount, unless both discounts are set to combine with product discounts. Shopify keeps one, and the code stays unused.
Get notified: Coming soonCheckout says
“WAX15 couldn’t be used with your existing discounts.”
Checkout X-Ray says
WAX15 wasn't applied. WAX15 wasn't applied to Selling Plans Ski Wax: the item already has Buy 2 wax, get 1 free (lab: automatic BXGY) ($24.95 vs $11.23). Only one product discount applies per item.
Why it happens
Two product discounts on the same item stack only when both are set to combine with product discounts. When either isn’t, the item gets one of them, and Shopify keeps the bigger saving.
In the lab (truth cart 07, 24 October 2026) three waxes cost $74.85. “Buy 2 wax, get 1 free” takes one wax off, $24.95; WAX15 would take 15%, about $11. Shopify kept the free wax: the customer pays $57.90. With WAX15 alone it would have been $71.63. Point at the product-discounts row to see where WAX15 would have landed.
What Checkout X-Ray reads
- Each discount’s kind and whether it combines with product discounts.
- Which cart items each discount applies to, and what the applied one took off.
- The cart priced again with each discount alone, for the two totals: what the customer would pay either way.
What to look at in Shopify
Both discounts’ combination settings, in Discounts. If they should stack on the same item, set both to combine with product discounts; if they shouldn’t, the customer gets the bigger one, as here. Combinations lists every pair like this in your store.
The sentence Checkout X-Ray writes for this reason, filled in for each cart: Lost wasn’t applied to item: the item already has won (amount vs amount). Only one product discount applies per item.
Answer the next one with an X-ray.
Install on Shopify
Add Checkout X-Ray from the Shopify App Store. It opens in your Shopify admin, on the Free plan.
Build the customer’s cart
Open the Simulator. Pick the products, type the code they used and the country it ships to, then calculate the price.
Read the answer
The price X-ray shows each layer, and every code that wasn't applied gets a sentence saying why. Save it as a test cart to have it checked again.
