Apps
To test and run apps before they hit the Microsoft Store, you can side-load apps to your or your organization's Teams. For more information about the different apps, you can find in separate manuals.
Control that users click-to-call function is set to Teams for the TEL (URL:tel) protocol. See what apps currently are availble here.
Side Loading
As an admin in your Microsoft organization, open the teams client and go to Apps in the menu on the left. Select Upload a custom app. If you want to upload the app for yourself, select the option at the top, "Upload for me or my…".
If you want to make the app selectable for everyone in your organization, select the lower option, “Upload [Organisation]".
Microsoft Teams admin center
To enable your users to side-load or allow them to install apps, you may need to make a change in your organization's admin center.
Go to https://admin.microsoft.com/
Click on the teams admin center and select "Teams apps" and "Permission policies".
Set the rules that suit your organization if it is to be all apps or the ones you choose.
Select the .zip file for the app you want to install and follow the on-screen instructions.
