WooCommerce add to cart not working

A WooCommerce product page holds a form. For a simple product the form sends the product ID and the quantity. For a variable product it sends a specific variation only after every option has a value, so a shopper who picks a color and skips the size sends an incomplete product. The store then answers with a notice above the product, or with nothing visible if the theme hides the notice. Stock is checked on the same request, so a quantity above what is left gets refused. A script error on the page can stop the form from sending anything.

• Pick every option on the product, click Add to cart, and read the notice that appears above the button.
• Check the stock for the chosen option, then the quantity field, which can be higher than the stock.
• Check whether the product is set to sold individually, which caps the quantity at one.
• Open the browser console at the moment of the click and note any script error that appears.

The shopper clicks Add to cart and one of three things happens. The page refuses the add and shows a notice that names a missing option, a limit or a stock shortage. The page shows nothing, because a script error stopped the form before it sent anything. Or the item goes into the cart, which means the button worked for that product and the fault lies elsewhere. Watch the click itself, and read the cart count right after it, not later.

Variable products carry a list of options such as color and size, and the form only knows which variation to add when each option has a value. A shopper who picks a color and skips the size sends a request with no variation, and WooCommerce asks for the missing option with a notice. On a phone the notice can sit under a sticky header. The fix belongs in the product, not in the button: every option needs a value a shopper can pick.

A size can also be listed with no price or no stock. WooCommerce does not sell a variation that has no price, so that size cannot be added however many times the shopper clicks. Check each variation on its own page in the admin, not only the parent product, because one empty size can break the button for that size alone and leave the rest of the product working.

Stock is checked when the click arrives, not only when the page loads. A product that had stock when the shopper opened it can be short when they click, because another shopper took the last pair in the meantime. The notice then says there is not enough stock for the quantity chosen. A product marked sold individually accepts one unit, so a shopper who types two gets a refusal. Read the quantity field before you blame the button, since a typed quantity above the limit fails on its own.

A simulated visitor opens the product from its link, picks the options the task names, and clicks Add to cart. The run records the notice text, a screenshot of the product page after the click, the address the page ended on, and any script error or failed request on that step. A click that does nothing shows as no change on the screenshot, with the error beside it when the browser logged one.

The run cannot tell you which option is missing in your catalog, or why a variation has no stock. Open the product in the admin, check each variation, and fix the one the notice names. Keep the product and the options the same between runs, so only your fix changes. Then send the visitor again and read the new notice, if there is one.

A variation added next season, a stock sync from another tool, or a theme update that moves the notice can turn a working button back into a silent one. Rerun the same visitor after each change, with the same options. Test one size from the shop page and one from the product page, since the two can take different paths.