DTMF not working - "3CX Desktop App for Windows" installation using system account

[gcf]

Hello,

I notice that DTMF is not working when "3CX Desktop App for Windows" is installed using system account.
There is no problem with DTMF when "3CX Desktop App for Windows" is installed using user account.

We are using Version:18.13.959 and 3CX Desktop App is deployed by Intune for 1500 users.
We decided to deploy the application using system accout because severals users can use the same computer.

Any ideas in order to resolve to issue ?

Thanks for your help.