Low conversion rate Shopify: find the step

A shopper on a product page has one question before the add to cart button means anything: can I get this in the version I want? They pick a size, and the page either confirms it or quietly fails. If the option they picked is sold out, the button may still say Add to cart and then do nothing, or it may be grayed out with no line saying why. If the preselected option is sold out, the photo and price shown first belong to something nobody can buy, so the shopper assumes the whole product is gone. They leave without trying the other sizes.

• Preselected option: is the size or color chosen when the page loads something you can actually sell today?
• Sold-out options: are they hidden, marked Sold out, or left clickable with nothing happening?
• Photo and price: do they change when the variant changes, or do they stay on the first option?
• Add to cart on a phone: is the button in the first screen, or pushed under a sticky header or an app banner?
• Feedback after the click: does the cart count or a small drawer confirm that the item went in?

Open the product in a private window and do not touch the options. Look at which size or color is already selected, what the price says, and what the photo shows. Then check whether that option has stock. Some stores open on the first item in the list, and that item is often the first to sell out. A shopper then sees a price and a photo for something they cannot buy, while the button still looks active. The wrong version is a default that is sold out with no label. The right version opens on the first option that can be bought, marks the sold-out ones beside the picker, and changes the photo and price when the selection changes.

A shopper who clicks Add to cart has made a decision, and the cart is where that decision is kept or dropped. The cart drawer or cart page has to show the item, the quantity, the subtotal and one clear button that goes to checkout. On a small screen a drawer can push that button below the fold, and a discount field can look like the place to pay. Shoppers also stop when shipping is missing, since the cost often appears only at checkout. Compare the number of visits that added to cart with the number that started checkout in your store analytics. A large gap there points to the cart, not to the product page.

Review widgets, popups, countdown bars and newsletter sign-ups get added one at a time, and each takes space. On a phone, a sticky header or a bottom bar can sit over the Add to cart button, so the button is in the page but not where a thumb can reach it. A popup that opens on scroll can also hold the page until it is closed. Check this at phone width: open the product, scroll to the button, and see whether anything covers it or moves it. Remove or move the block that does it. A new app or a theme update can bring the same problem back, so check the product page again after every change.

Stores change after the first fix. A new review app, a popup, a theme update or a sold-out size can each move the button or empty the default option again, usually without anyone on your team seeing it. Run the same shoppers through the same product after each change, and check whether they reached the cart. Paid runs can open a protected staging copy behind a site password, so a change can be checked before it goes live.