Screen sharing using multiple monitors in Citrix and terminal server environments

State of knowledge

July 2021. Citrix and terminal server environments

Observation

If several monitors are connected to the PC with the ProCall Enterprise client installed, only the content of one screen can be shared.
Both monitors are available in the screen sharing preview, but show the same content (of the primary monitor).

Possible reason

Terminal Server/Citrix Server does not support Direct3D.
https://en.wikipedia.org/wiki/Direct3D

Solution/Procedure

Direct3D support can be disabled on the server where ProCall Enterprise client is installed.

Create registry entry

On the server where the ProCall Enterprise client is installed, create DWORD value "AVScreenCaptureMode" and set it to 1 (decimal).

Example

Computer\HKEY_CURRENT_USER\SOFTWARE\ESTOS\UCServer4\CtiMain
AVScreenCaptureMode = 1

This disables Direct3D support.

Then restart the ProCall client.