Add to cart button not working: find the cause

The cause is often a step they did not know was needed: the size was never picked, so the store takes the click and shows its warning somewhere they did not look. Or a script failed earlier on the page, so the click never sends a request. The owner tests logged in, with the size remembered, on a desktop, and the button works. A stranger arrives from an ad on a phone with nothing saved, and the same button sits under a sticky bar.

• Is every option set, such as color or size, or does the button still say to choose one?
• At phone width, does a cookie banner, chat bubble or sticky bar cover the button?
• Does the browser console show a red error at the exact moment you click?
• Does clicking add a request in the network tab, and what status does it return?
• Is the item in the cart page, even if the cart icon did not change?

The shopper picks a color and a size, then presses the button. If the store needs a size and none was picked, many stores take the click, show nothing beside the button, and put the warning above the fold. The second press gives the same silence. The shopper scrolls for the cart icon, sees the count has not moved, and leaves.

From the outside, every cause looks identical: the button is pressed and nothing changes. A missing size is a choice the shopper did not make. An out of stock variant is a stock count the store holds. A script error is code that failed before the click was wired up. A rejected request is the cart server refusing the add. Each needs a different fix, so a generic fix, such as clearing the cache, usually spends time without touching the cause.

Open the product page in a normal browser window, not one logged in as an admin. Open the developer tools and go to the Console tab. Press Add to cart once, with the options set the way a shopper would set them. A red error at the moment of the click names a file, often a third party script. No error and no reaction points toward the options or an overlay.

Next, open the Network tab and press the button again. No new request means the click never reached the cart. A request with a 4xx or 5xx status means the cart refused the add. A successful response with no change in the cart icon means the button worked and the display did not. Open the cart page in a new tab to settle it: the item is there or it is not.

A simulated test runs the same click with a visitor who arrives the way your shopper does. You give the page address, the task and who the visitor is. Name how they arrive, such as a keyword or ad text, and the report compares what the ad promised with what the page shows. Each step records JavaScript errors and failed app requests, with a screenshot.

The run stops where you tell it to, such as at the cart, and it never pays with a real card. Visitors cannot sign in with Google or single sign on, so a store that only allows those stops the run early. A bot check can stop a visitor too, and the report then marks that visitor as blocked by the site. The test does not read your analytics, so it cannot tell you what share of visitors reached the button.

Checkout flow testing

After you fix the size warning or the script that failed, send the same visitor through the same product page again. Each run shows whether the visitor reached the cart and which step stopped the ones who did not. Owners keep testing for a store behind a site password and for each preview deploy.