Shopify Black Friday problems: the ones that break stores, and the fixes

The customer enters your sitewide code and a loyalty or creator code, and checkout keeps only one. Shopify's own message is "Some discount codes couldn't be used together. We applied the best combination". Every discount has its own combination settings, and a pair only stacks when both allow it. Shopify's discount combinations guide adds conditions merchants miss: combining product with order discounts needs a store without checkout.liquid customisations, two product discounts on the same line item needs Shopify Plus, and a customer can use at most five product or order codes plus one shipping code on an order.

Decide the stack you actually want, set it on every discount involved, and test it in a real checkout. The full rule set and the workarounds are in why Shopify discount codes still don't stack on Black Friday, and the margin side is covered in how Shopify discount stacking works in 2026. If the second discount only exists to sweeten the deal, a free gift above a spend threshold often does the same job without a second code fighting the first.

Checkout shows "Shipping not available" or "Your order cannot be shipped to the selected address" for some customers and not others. Black Friday makes this more likely for a specific reason: Shopify's shipping troubleshooting guide says price-based rates use the cart value after discounts, so a sitewide discount can push a cart out of the tier that used to catch it. Weight tiers with a ceiling, countries sitting in a market with no rates, and products in the wrong shipping profile do the rest.

Rerun your shipping tests with the promotion switched on. The step-by-step diagnosis is in Shopify shipping not available at checkout.

The campaign sends people to the homepage or a product page, and they have to find the variant, add it and remember the code. Every extra step loses some of the traffic you paid for.

Shopify's cart permalinks can pre-fill products and a discount code, so the click opens a cart that's ready to buy. The Black Friday checkout playbook walks through building those links for Meta, email and SMS, with tracking and purchase limits.

Shopify hosts and scales the storefront itself, so when product pages feel slow under load, look first at the scripts running in the shopper's browser: review widgets, upsell apps, chat, several tracking pixels, and third-party services those scripts call, which have their own capacity limits.

Audit the app embeds and tags on your top product pages, remove the ones nobody can justify, and move the rest out of the critical path. Shopify speed fixes that actually improve conversion covers what to cut first. If a script is breaking the page rather than slowing it, see Shopify app conflicts breaking the storefront.

Someone installs a countdown app, edits the cart drawer or publishes a new theme copy the week of the sale, and the add-to-cart button or cart drawer stops working on one template. The change looked fine in the editor because the editor was previewing a different product or market.

Set a change freeze before the sale, keep a known-good duplicate of the published theme, and test on the live theme after any exception. Add to cart or product content missing and theme changes not showing live cover the two ways this usually shows up.

Overselling usually comes from variants left on "continue selling when out of stock" after a preorder, or from a warehouse or ERP sync that updates on a schedule while orders arrive every few seconds. False sold-outs usually come from stock held at a location that can't ship to the buyer's zone, which Shopify started enforcing more strictly in 2025.

Check the inventory policy on every campaign SKU, shorten or pause the sync window during the sale if your tools allow it, and confirm which location serves each market. Products showing sold out when in stock and Shopify Markets with multiple warehouses cover the location side.

The gift message field, the upsell or the delivery-date notice you set up for the sale isn't in checkout. Usually the block was created in the app but never placed in the checkout editor, or its display rules don't match the market or cart being tested.

Place the block, check its conditions, and test with a real checkout in each market. The editor preview doesn't show market conditions. Checkout Blocks not showing has the full check order.

Dozens of cheap orders arrive from new accounts in a few minutes, often flagged as risky. That's card testing: scripts checking whether stolen card details still work. Shopify's bot protection blocks known bots from checkout, and Shopify says it's requested through Plus Support.

Hold fulfilment on high-risk orders, cancel and refund the confirmed test orders, and look at how the bots are reaching checkout. Rapid-fire fake Shopify orders covers containment and automation.

Add-to-cart rate jumps while orders don't, and sessions arrive from places you don't sell to. Bot traffic skews the numbers you'll be using to judge the campaign, and on limited-stock drops it competes with real customers.

Filter it out of reporting before the sale so your baseline is honest. How to detect and stop fake add-to-carts explains the signs and the filters.

International shoppers from your ads see one currency on the product page and another at checkout, or a local payment method they expected is missing. Market currency settings and payment gateway support decide this, and neither is visible from the storefront.

Test checkout from each market you advertise in. Shopify currency changes at checkout and local payment methods not showing cover the causes.

Orders are created but some customers never get the confirmation, so they email to ask whether the order went through. Missing sender-domain authentication is the first shared cause to check, and a customised notification template can fail for only some orders.

Send test notifications to two different mail providers and check your DKIM, SPF and DMARC records before the sale. Order confirmation emails not received has the checks.

A big order week also means a big week of "where is my order" and "can I change my address" messages, arriving while the warehouse is behind and carriers are slow. Customers who can't check out because of problems 1, 2 or 10 write in too.

Put realistic dispatch dates on product pages, in the cart and in the confirmation email, make the order status page easy to find, and decide in advance what gets answered automatically and what goes to a person. The Black Friday support surge guide covers how to handle that queue, and your support inbox is a CRO backlog explains how to turn the repeat questions into storefront fixes afterwards.

Run this on the live theme with the promotions switched on. Use a new checkout each time, because Shopify notes that an abandoned checkout keeps the shipping rates from when it was created.

If a step fails and the cause isn't obvious from the guides above, that's the kind of fix we take on through the Shopify fix task library. For the broader prep list, see what to fix before peak traffic.