FileRun uses by default Bitly.com for shortening the shared links. Please follow these steps to enable the feature:

1. Log in to Bitly and navigate to the OAuth Apps page
2. Click “Generic Access Token”. You will be asked to enter your Bitly password.
3. Copy the generated access token and paste it into FileRun's control panel, under Third party services

You can configure FileRun to use any other URL shortening service. Please see the $config['app']['weblinks']['custom_url_shortener'] directive on the advanced configuration page.