In Dossier, you and anyone else on your team who chats with visitors on your website needs to have the “chat” role.
To assign a team member manually to chat support in Dossier, first, invite the team member to join Dossier. On the My Team page, move the CHAT slider from OFF to CHAT. Note that if you added a team member to chat during the signup process, the slider will be in CHAT automatically. You can remove the team member from chat by simply moving the slider to OFF.
See Manage Team Members.
NOTE: If you add a new team member to Dossier with the Chat role, then you need to disconnect and reconnect Slack on the Apps page to add and make the new team member appear in Slack chats.