Customers add to cart, click pay, and the page spins — or errors, or silently loses the order. Because the store looks fine in the morning, it's easy to blame 'a random glitch'. But checkout failures almost always have a recognizable cause. Here are the six to check, in order, and the sign that says you now need a specialist.
Check these first, yourself
Reproduce it yourself on a phone and a desktop — take notes on exactly where it breaks.
Check the payment gateway's dashboard for declined or 'session expired' charges.
Look at your server logs for the exact moment of the failure — the error message is usually right there.
Test the cache — A ready-made copy of your pages kept warm so the server doesn't rebuild everything on every visit.: if it disappears with caching off, the cart/session is being cached incorrectly.
Watch what happens during a sale or spike — are payments failing only under load?
Should you fix it yourself or call a rescue?
Still have questions?
My payments pass in the test but fail for real customers. Why?
Test cards bypass the real-world failure points: payment processor rules, 3D-Secure, geolocation blocks, and currency conversions. 'Works in the test' and 'works under real traffic' are different things.
Could it be a plugin conflict?
Very common — a discount, tax, or shipping plugin — An add-on that extends your CMS; outdated or abandoned plugins are the most common way sites get hacked.'s update breaks the checkout flow quietly. That's why the log moment-of-failure matters: it names the component that threw the error.