Teams is best collaboration tool in the market and customers are migrating away from Skype for Business . But there is a chance you might get stuck in switching the coexistance mode from islands to Teams only. From the GUI you get an error with no proper details.
When you try from powershell you get the below error.
“This organization cannot be upgraded to TeamsOnly at the tenant level because there is an on-premise deployment of Skype for Business detected in 1 or more of its sip domains, localerror.com. Users can be individually upgraded to TeamsOnly using either Move-CsUser (if the user has an on-premises Skype for Business account) or Grant-CsTeamsUpgradePolicy (if the user is homed in Skype for Business online). “
Now in my scenario, I never had a Skype for Business Server on-prem. The only option for me was to disable the sip domain which was being shown in the error message.
Disable-CsOnlineSipDomain -Domain localerror.comIt takes some time depending on the number of users present. Once completed I ran the upgrade command again.
Grant-CsTeamsUpgradePolicy -PolicyName UpgradeToTeams -GlobalIn my case I got the error again for other domains in my tenant so I had to repeat the disable action. Once all the sip domains where disabled I was able set the global policy to Teams Only.
Hope it helps !