Shopify Checkout Bug Fixing: 12 questions answered.

A checkout button that spins forever, a failed AJAX cart, or a redirect loop / 404 is almost always a theme JavaScript conflict, a custom cart.js, a stale cart/add.js call, a duplicated event handler, or an app that hijacks the checkout redirect. We open the browser console and network tab on a preview theme, find which script is blocking the POST to /checkout, and resolve it, often an app conflict.

Most single, well-defined checkout bugs are a flat $99 Quick Fix (about 4 hours at $25/hr), turned around in 24-48 hours. A batch of issues, or one stubborn root-cause like a full checkout.liquid → Checkout Extensibility migration, is a $499 Bug-Fix Sprint (~20h @ $25/hr). If checkout is down right now or you need standing peak-season cover, the Emergency / Retainer tier is custom-quoted. You always get the fixed price before any work starts.

The usual culprits: a discount combinations rule blocking it from stacking, a Shopify Function that wasn’t deployed or has a logic bug, a discount that only targets the cart but not the checkout, or an old Script Editor script that stopped running after the Checkout Extensibility move. Errors like “This code isn’t valid” or a discount that shows in cart then vanishes at payment point to one of these. We trace which layer is dropping it and fix it.

Yes. Every checkout fix comes with a 14-day re-fix guarantee, if the same bug returns within two weeks, we fix it again at no extra charge. You also get a short write-up of the root cause and the change we made. If you want ongoing cover through a launch or peak-sales period, our Emergency / Retainer tier adds 24/7 on-call and monthly checkout health monitoring. For broader incidents, start at our emergency e-commerce bug fixing hub or the urgent Shopify bug fixing page.

Emergencies, checkout down or dropping orders, get triaged in under 4 hours, any timezone. A standard single checkout bug (a discount not applying, a missing payment method, one broken shipping rate) is usually fixed in 24-48 hours. Larger work like a checkout.liquid migration runs across a short sprint. We confirm the turnaround when we quote, so there are no surprises.

Yes, you need to migrate. Shopify is retiring the old checkout.liquid file and the Additional scripts box in favour of Checkout Extensibility, checkout UI extensions, the branding API, Shopify Functions and web pixels. After the deadline, customisations living in checkout.liquid stop working. We audit what your old checkout did (custom fields, scripts, upsells, tracking) and rebuild each piece the Extensibility way before the cut-off. See our Shopify theme & Liquid bug fixing page for related Liquid work.

“No shipping rates available” usually means the buyer’s address doesn’t match any shipping zone, the product’s weight or shipping profile excludes it, or a carrier-calculated rate (Carrier Service API) is timing out or returning an error. Overlapping or duplicated zones can also silently knock out rates. We audit your shipping profiles, zones and any carrier/app integration, then reproduce a real cart to confirm the fix.

A payment method disappears when it’s restricted by country, currency or customer rules, the express wallet (Apple Pay / Google Pay) needs domain verification, the gateway isn’t activated for that market, or a payment customization Function is hiding/reordering it. Shop Pay also needs the customer accounts and the right activation. We check each condition against a real test checkout to see exactly why it’s not rendering.

Shop Pay or express checkout (Apple Pay, Google Pay, PayPal express) glitches when customer accounts aren’t configured correctly, the express button conflicts with a theme cart drawer, discounts/shipping don’t carry through the accelerated flow, or a checkout customization clashes with the wallet. We test the full accelerated path on a preview store, isolate the clashing setting or script, and make the express flow match your standard checkout.

Both, safely. We prefer a duplicated/preview theme or a development store to reproduce and fix without touching live orders. For account-level settings (payments, shipping zones, discounts) we use limited Collaborator or Staff access with only the permissions needed. You can revoke access the moment we’re done. We confirm exactly what access we need before starting.

Yes. “Extension failed to render”, a blank custom block, or a console NetworkError in a checkout UI extension usually comes from the wrong extension target, missing API access scopes, an unhandled async error in the extension code, or a deployment that never shipped. We debug the extension against Shopify’s preview tooling, fix the target/scope/logic, and redeploy.

Yes. We never debug against your live checkout. We reproduce the fault on a duplicated/preview theme or a development store, fix it there, run the full funnel through regression testing, and only then publish. For checkout UI extensions we use a preview deployment. Your live orders keep flowing while we work, and you approve the change before it goes live.