When I add an item in the cart, there is another item there already.

« Return to Shopping Cart Buttons

Each buyer's cart persists for up to 10 days after their last cart view, so if you're testing your own Add to Cart buttons, anything you'd added to your cart in the past 10 days would still remain in your cart today. You could use a Private/Incognito browser window to test your cart from a "clean slate" if you wish.