Select your app from the list (or create one if you don't already have one).
Select Authorization in the left menu.
Next to OAuth 2.0 (3LO), select Configure.
Enter the Callback URL. Set this to any URL that is accessible by the app. When you implement
OAuth 2.0 (3LO) in your app (see next section), the redirect_uri must match this URL.
Click Save changes.
Note, if you haven't already added an API to your app, you should do this now: