Most Shopify merchants lose sales to checkout problems they don't know exist. The storefront looks fine. Revenue is just slightly off. No one complains because frustrated customers don't email — they just leave.
Here are the 10 most common Shopify checkout issues we've found after testing thousands of stores — ranked from most impactful to most subtle.
1. Checkout fails to load entirely
The most severe failure: the checkout page returns a 500 error, a blank page, or an infinite loading spinner. This is usually caused by a theme update that introduced a Liquid syntax error, a conflicting app, or a Shopify infrastructure issue.
Fix: Check your Shopify error logs in Admin → Settings → Notifications → error reports. If it's a theme issue, restore the previous theme version. If it started after an app install, temporarily uninstall the last app added.
2. Add to cart not working
Clicking 'Add to Cart' does nothing — the button just spins, or the cart count doesn't update, or no feedback is given to the customer at all. Usually caused by a JavaScript conflict between the theme's cart JS and a third-party app script.
Fix: Open browser DevTools console and look for JS errors on the product page. Common culprits are review apps, upsell apps, and loyalty apps that inject scripts onto product pages.
3. Slow checkout load time (over 3 seconds)
Studies consistently show that checkout pages loading over 3 seconds lose 40%+ of their potential conversions. Slow checkouts are most commonly caused by too many third-party scripts loading synchronously on the checkout page.
Fix: Review which apps have scripts loading on checkout pages. Each app installed in Shopify can inject scripts. Remove apps you no longer use, and ask remaining apps to use async script loading.
4. Payment form not rendering on mobile
The card number, expiry, and CVV fields don't appear on mobile, or appear but can't be tapped. Mobile checkout failures are particularly hard to catch because most merchants test on desktop.
Fix: Test your checkout on an actual phone, not just a browser resize. Look for CSS issues where the payment iframe is hidden or incorrectly positioned.
5. Discount codes not applying
Customers enter a valid discount code and see an error, or the discount shows applied but the total doesn't change. Most commonly caused by conflicting discount rules — such as a code that's been expired, restricted to certain products, or conflicting with an automatic discount.
Fix: Test every active discount code manually. In Shopify Admin, check for discount conflicts — Shopify doesn't allow stacking of most discount types.
6. Shipping rates not calculating
The customer reaches the shipping step and sees no shipping rates, or sees an error. This blocks checkout entirely. Usually caused by Shopify's carrier-calculated shipping having a connectivity issue, or by products not having a weight assigned.
Fix: Verify all products have a weight set. Check Shopify Admin → Settings → Shipping and delivery to confirm your shipping zones and rates are configured correctly.
7. Checkout stuck in a redirect loop
Customers are bounced back and forth between pages without being able to progress. Often caused by conflicting redirect rules, a broken custom domain configuration, or a password-protected checkout.
8. SSL certificate errors
Browsers show a 'Not Secure' warning or block access to the checkout entirely. Shopify handles SSL automatically for myshopify.com domains, but custom domains can have SSL issues — especially when the domain was recently migrated or the DNS was changed.
Fix: In Shopify Admin → Domains, check that your custom domain shows 'SSL certificate pending' has resolved to active. If not, remove and re-add the domain.
9. Thank you page not loading after purchase
The customer completes their order but hits an error or blank page instead of the thank you/order confirmation page. This doesn't technically prevent the sale, but it breaks confirmation emails (sometimes) and tracking pixels, and causes customers to contact support thinking their order didn't go through.
10. International checkout issues
Customers in certain countries or using certain currencies can't complete checkout. Most common with markets-enabled stores — a specific currency or payment method that works for some countries isn't available for others, but the store shows those customers pricing in that currency anyway.
How to check for all of these at once
Rather than checking each issue manually (which takes 15–30 minutes per store), you can run an automated checkout test that simulates the full purchase flow and flags every issue in a single report.