The app can't be loaded because of cookies or same site cookie issues
If you get an error message from Shopify saying that "The app can't be loaded because of cookies ...". It means that you have not enabled third party cookies in your browser.
If you are using Chrome with incognito mode, make sure that the "Block third-party cookies" setting is disabled (see screenshot).
The app requires third party cookies to know when you are logged into Shopify, otherwise we have no way of knowing who is logged in.