Are you sure that your organization has enabled Microsoft Team Service ?. you are trying to download the app and starting and getting below error !!!
you know that it’s available to Office 365 commercial customers with one of the following plans:
Business Essentials, Business Premium, and
Enterprise E1, E3 and E5. Microsoft Teams will also be available to customers who purchased.
So I login to my O365 portal to make sure that license is properly assigned. I fund that “Team” is not enabled under O365 Enterprise E3 license which is not letting me to download the app.
To resolve it, we need to enable it, and now we are good to go !