...
3. In Workspace Settings, click on the “Installed apps” link under “Apps and Features”.
...
Please note: you will to enable development mode to install the app. Please ensure that the “Enable development mode” checkbox is selected.
4. Next click on the “Install app from URL” in the top-right corner of the page, which will open a popup dialog.
...
With the app created, the following link will authorise the app for a selected workspace. (You may be asked to login if you haven't done so already.)
If the app is already registered:
otherwise: