Footsites use a system called "cart holds" which keeps the release fair. Essentially, when you cart the product, the site gives you 5-10 minutes to checkout. During this time, it is normal for your tasks to show ATC Failed [OOS]. This does not mean the product is out of stock because once a user/task fails to checkout within the given 5-10 minute window, their cart is lost and from there, your tasks will attempt to add the product to cart again. That is why we recommend keeping your tasks running even though it shows out of stock.
Cart holds are usually enabled during Initial drops and disabled for restocks.
Paypal checkout is highly recommended to be used on footsites. Despite the slow process, footsites have cart holds so your tasks will have plenty of time to check out using PayPal. If PayPal fails, this 5-10 minute timeframe will still allow for the fallback of Card checkout. For more information, click here