Here are the details to do the manual configuration for Skype for Business while facing the error in logging.
Some times, the Skype for Business won’t be able to connect automatically and at that time we need to provide the configuration for the connection settings. Try the following steps:
Internal Server Name: sipdir.online.lync.com:443
External Server Name: sipdir.online.lync.com:443
Original Post https://codethecoffee.wordpress.com/2017/03/27/how-to-manually-configure-skype-for-business-during-sign-in/