Hi Ryan,
Is the URL set in the properties of this page? Setting this would result in something like https://myapp/{url}
See https://docs.mendix.com/refguide/page-properties#2-3-6-url
It looks like your app is using a modeled login page that is accessible to anonymous users. Therefore, by default, you won’t have a direct URL to that page.
You might not need to set that constant. It is only used to redirect a user to log in when they don’t have access to a given deep link. If that’s not a use case for you, then you don’t need to set the constant. If you do, then it can just be index.html, as long as the LoginPage is the anonymous user’s home page. If it is not, then add a URL in the property in Sjors’s answer and set that URL as the LoginLocation