Browsers are normally fully adapted and configured to allow purchases on their portal. If you notice that during the purchase process, the products are not being added to the basket, you must change the security settings of your browser. Tools > Internet Options > Privacy and you can assign a medium level to allow cookies.
It is possible that it could also be due to a problem with cookies, in which case you can try without being logged in to the store (guest), incognito browsing or using another browser/device.