Box for Teams Integration for Private Channels
Today, Box for Teams Integration does not support Private Channels.
https://support.box.com/hc/en-us/articles/360044673394-Box-for-Teams-FAQ
Many customers are using Private Channels and need full integration between Box and Microsoft Teams. We do want Microsoft and Box to work together to improve it.
71
votes

This limitation is due to Microsoft’s platform not allowing integrations to surface as messaging extensions (Box icon to upload and share documents). Until Microsoft supports this for third parties, Box is unable to deliver this functionality. We are working with Microsoft but there is no timeline for delivery at this point.