You must call the Connect-MicrosoftTeams cmdlet before calling any other cmdlets.

You must call the Connect-MicrosoftTeams cmdlet before calling any other cmdlets. is the message of the team management cmdlets in the MicrosoftTeams module (Get-Team, New-Team, Add-TeamUser, Get-TeamChannel, ...) when there is no Teams session. Connect, then run the command again:

Connect-MicrosoftTeams
Get-Team -DisplayName "Marketing"

Reproduce it

MicrosoftTeams 8.0.0 imported, no connection:

Import-Module MicrosoftTeams
try {
  Get-Team -DisplayName "Marketing" -ErrorAction Stop
} catch {
  $_.Exception.Message
  $_.Exception.GetType().FullName
}

You must call the Connect-MicrosoftTeams cmdlet before calling any other cmdlets.
System.UnauthorizedAccessException

The exception type is System.UnauthorizedAccessException, so catch [System.UnauthorizedAccessException] catches it in scripts.

Two messages, one cause

The module contains two families of cmdlets with different not-connected messages:

Both are fixed by Connect-MicrosoftTeams. If the error persists right after connecting, check that the script did not open a new runspace (Start-Job, ForEach-Object -Parallel) where the session does not exist.

What the message means

The MicrosoftTeams module keeps the signed-in session in memory for the current PowerShell runspace. Every team cmdlet checks for that session before it sends anything; when none exists it throws this message as a System.UnauthorizedAccessException. The command did not reach Microsoft Teams, so nothing was read or changed. The wording "before calling any other cmdlets" is generic: importing the module and running Get-Help or Get-Command still work without a session.

How to recognise each cause

Fix and confirm

1. Run Connect-MicrosoftTeams. Interactive sign-in opens a browser; on a server without one, add -UseDeviceAuthentication.
2. Watch the output: a successful connection prints the account, environment and tenant ID. An error at this step (for example, conditional access or MFA) is the real problem to solve.
3. Rerun the command, for example Get-Team -User you@contoso.com. Results, or an empty result without an error, confirm the session.

Handle it in scripts

Because the exception type is fixed, a script can connect only when needed:

try {
  $null = Get-Team -User admin@contoso.com -ErrorAction Stop
} catch [System.UnauthorizedAccessException] {
  Connect-MicrosoftTeams
}

For scheduled jobs, connect with a certificate at the start of the script and avoid moving Teams work into separate jobs. The Cs cmdlets have their own wording for the same situation: Session is not established. All sign-in options are on Connect-MicrosoftTeams.

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