MS Teams: can not fetch channel messages with Graph API using an application token

Question

I have created a test application which is requesting adminconsent from a MS teams admin with the following scopes :

openid offline_access channelmessage.read.group channelmessage.read.all chat.read chat.readbasic chat.readwrite user.read.all channel.readbasic.all directory.read.all group.read.all groupmember.read.all organization.read.all people.read.all presence.read.all team.readbasic.all

I am using an application token to fetch ms teams organization data like users, channels, teams etc. I have managed to fetch with Graph API the user, channel, teams data of an organization, but when I tried to fetch messages with

https://graph.microsoft.com/v1.0/teams/team_id/channels/channel_id/messages

I am getting the following error:

{
  "error": {
    "code": "UnknownError",
    "message": "",
    "innerError": {
      "date": "2021-03-03T22:23:47",
      "request-id": "a279044a-ab9e-4c18-af71-5a65ea7cee86",
      "client-request-id": "a279044a-ab9e-4c18-af71-5a65ea7cee86"
    }
  }
}

Answer 1

When you are using application permissions you need to you must request access.For details, see Protected APIs in Microsoft Teams.