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:
For Skype for Business Server 2019, install the July 2019 cumulative update 7.0.2046.123, Web Components Server.
For Skype for Business Server 2015, install the January 2019 cumulative update 6.0.9319.537, Web Components Server.