In a Microsoft Skype for Business Server 2019 or Skype for Business Server 2015 environment, you're located in a network site that's enabled for Location-Based Routing (LBR). When you make an outbound emergency call by using a Skype for Business on Mac client, the call fails. In addition, the Skype for Business for Windows client isn't affected.
This issue occurs because Skype for Business Server doesn't assign a correct policy to the user to send the calls through in this situation.
To fix this issue, install one of the following updates: