This issue occurs when you click the call me option to join a meeting as an anonymous user from Microsoft Lync Web App. When this issue occurs, the call is dropped immediately or disconnects after you try to answer it.
This issue occurs because the public switched telephone network (PSTN) dial-out is initiated from Unified Communications Web API (UCWA) instead of from Audio Video Multipoint Conferencing Unit (AVMCU) in Lync Web App.
Article ID: 3078400 - Last Review: Jul 20, 2015 - Revision: 1
Microsoft Lync Server 2013