UCWA client can’t make a P2P call or join a conference when EnableExternalAccessCheck is True and EnableOutsideAccess is False in Skype for Business Server

You set the EnableExternalAccessCheck parameter to True and set the EnableOutsideAccess parameter as False in Microsoft Skype for Business Server 2015. In this scenario, a Skype for Business on Mac user can’t make a peer-to-peer (P2P) call or join a conference. This issue only occurs after you install the July 2018 cumulative update for Skype for Business Server 2015 (CU7).

This issue also occurs in Skype for Business Server 2019.

To fix this issue, install one of the following updates:

To work around this issue, you can enable the EnableOutsideAccess parameter in an external access policy or disable the EnableExternalAccessCheck parameter in a platform service settings configuration.