Mentions gives Atlas an ability to directly notify users that something need their attention. I It can be a pull requests that need to be reviewed by them or a build that has failed for their changes (commits).

...

When bot mentions you - you will may have notification about unread message from your Hangouts Chat app (it depends on your app settings). Also a , the unread message badge will appear in specific chat rooms, see below.:

...

Linking Hangouts Chat user account with Bitbucket Cloud account

@Atlas does not know how to properly recognize users from Bitbucket in Hangouts Chat room unless each user will connect both Hangouts Chat and Bitbucket/Atlassian accounts.

If a particular user want wants to be mentioned, then he should then login to Bitbucket from the chat (any room or private chat with Atlas will be good).

...

After clicking a link Configure you will be presented an auth authorization page within Bitbucket. Accept a scope and choose appropriate Bitbucket acocunt account - it should be the account you want be mentioned in chats.

...