My discount is not applying at checkout
Work through the five usual causes: the schedule window, the stacking both-sides rule, the store-wide discount limit, targeting and counting expectations, and your plan's live-campaign quota.
When a discount you expected does not appear at checkout, the cause is almost always one of five things, and the app can tell you which. Start with the simulator: build the exact cart you are testing and it will show you what applies and why. Then check the causes below in order.
1. The campaign is not live right now
Only a live campaign discounts anything. Check its status: scheduled means the start time has not passed yet, ended means the end time has, paused means someone paused it. Times run in your store's timezone, so a campaign that "should have started" may be a timezone reading of the date. See the schedule troubleshooting page for the details.
2. Another discount is blocking it
Two discounts apply to the same order only when each allows the other's class, product, order, or shipping. This is mutual: if either side says no, only one of them applies. This includes Shopify's native discounts and other apps' discounts, not just your Stackable campaigns.
When two eligible discounts do not both opt in, Shopify applies the single better deal, never both. So the campaign that is "not applying" may simply be losing to a bigger discount that is. If both campaigns are live but shoppers only ever get one of them, see the dedicated page "Two campaigns, only one applies".
Open both campaigns and check the three "Combine with..." switches on each. For a product campaign to work with an order code, the campaign must allow order discounts AND the code must allow product discounts. The app also flags stacking conflicts between your own campaigns on the dashboard.
3. The store-wide automatic-discount limit is full
Shopify allows at most 25 active automatic discounts per store, shared store-wide across Shopify's own automatic discounts and every discount app you have installed. If other apps or native discounts are running automatically, those count against the same 25. Pause automatic discounts you are not using, in Stackable or elsewhere, to free slots. A campaign you publish with the Discount code method does not use one of these slots, so a code campaign is never blocked by a full slot count.
4. The cart does not qualify the way you expect
- Targeting: only targeted items count toward thresholds and receive rewards. An excluded item does neither.
- Counting: "buy 3" depends on the counting mode. Three different products only qualify under "Across matching products" or "Whole cart", not under "Per product".
- Spend thresholds: Cart Goal and Free Shipping measure the whole cart subtotal. Free Gift is the exception, measuring only your targeted items, and the gift itself never counts toward its own threshold.
- Buy X Get Y set basis: with the default margin-safe basis, a "buy 3 get 1" set needs 4 items in the cart, 3 paid plus the 1 that becomes free.
5. Your plan's live-campaign quota is full
Each plan caps how many campaigns can be live at once. A campaign over the quota shows as blocked in the app and does not discount anything until a slot frees up. Pause another campaign or upgrade the plan; the blocked campaign then goes live.
Verify with the simulator
The simulator runs the same logic as checkout against any cart you compose, and the preview matches what checkout produces. If the simulator applies the discount but your storefront does not, compare the carts: the difference (an item, a quantity, a currency) is the cause.