To chat with the members of your organization, the members need to be enrolled and linked with that organization. The organization's administrators will enroll members as users. But, users also have to individually agree to be part of the organization by linking their account to the organization.
To link an account to an organization, navigate to My Account > Linked Account
The Linked Account page, shown below, will allow you to check the box to link the organization. Click the SAVE button to save your preferences.
Enabled users can either select or unselect to link the organization with this account.
Once an organization selects and links all its members, the members will be able to chat with each other. All linked member accounts will be visible to you in the chat window.