The Dropbox authorization URL is specific to your app and is composed of your app key, redirect URI, response type, and state (it looks something like https://www.dropbox.com/oauth2/authorize?client_id=...&redirect_uri=...). Each of the Dropbox SDKs contains a method that will help you generate this URL when you need it.
Then i build my own url:
https://www.dropbox.com/oauth2/authorize?client_id=fo7d5lzzuql1161&redirect_uri=https://localhost/test/dropbox
And i get this sad cat no matter what i do, i have enabled the 500 users for the development, added the icons and description to the branding section.

Thanks.