8x8 has a feature called Meetings included in both the phone and PC version of the app.
The Meetings feature allows you to have video calls with participants inside AND outside of the Town.
In 8x8, the 'Meetings' feature is displayed as a camera icon.
Two ways to start a meeting are by scheduling a meeting or using 'Meet Now'.
Scheduling a Meeting- If you are scheduling a meeting (especially with external users), the best way is to copy the link for your personal meeting space from 8x8 (image below).
Then from your Zimbra calendar create a new meeting invite and add the link in the body of your invite.

It has been found that creating a meeting invite via email makes things easier as all required information is in one place.
Meet Now- The other option for internal users is to search for a user by clicking the magnifying glass, click the three dots then select 'Meet now'.
Additional information can be found at the following links: