Resolve Skype for Business connectivity and sign-in issues.
The Office 365 DNS setup must be completed. A valid Skype for Business license muste be assigned in the Office 365 Admin Portal and the latest version of Skype for Business should be installed.
If the above fails, then follow the steps below:
Try to sign into Skype for Business again. If none of this helps, contact your administrator to open a case with Microsoft.