How to autorize everyone to participate to the chat on teams

Thanks for asking question! For a Communication Services user that joins a Teams meeting as a guest user can access the meeting's chat only when they have joined the Teams meeting call.

You may refer to the Teams interop documentation to see how to add a Communication Services user to a Teams meeting call.

To further elaborate on Teams interoperability this feature is currently in private preview and to enable this feature for your Communication Services resource, please email acsfeedback@microsoft.com with:

1. The Subscription ID of the Azure subscription that contains your Communication Services resource.
2. Your Teams tenant ID. The easiest way to obtain this is to obtain and share a link to the Team.

Please note that you must be a member of the owning organization of both entities to use this feature.

After enabling the Teams interoperability, a Communication Services user can join the Teams call as a guest user using the calling client library. Joining the call will add them as a participant to the meeting chat as well, where they can send and receive messages with other users on the call.

Reference: https://video2.skills-academy.com/en-us/azure/communication-services/quickstarts/chat/meeting-interop#enable-teams-interoperability

Please let us know if you have further query on this.