Custom link
From MoodleDocs
If you have an existing communication provider that is not connected to Moodle LMS, the 'Custom link' can be set as the provider. Simply provide a URL in the 'Custom link URL' field and save your changes. Use the room access icon to access your communication room. Look for the icon towards the bottom of you screen, above the information icon.
Please note, the 'Custom link' provider is not an integration between Moodle and chat system. This allows everyone to use the communication provider regardless of the plugin being available in Moodle LMS.