If there is already a "default app" set in Windows 10 for the "TEL" protocol, then the installation of the new Desktop App won't overwrite the default app.
This is a limitation of Windows 10.
We are checking though to see if there is some way we can detect this and at least prompt the user that there is a different default app selected and how to change it.
The instructions on how to change it on Windows 10 are:
- Open Windows 10 settings (not Control Panel)
- Search for "Default Apps"
- Scroll to the bottom and click option "Choose default apps by protocol"
- Find "TEL" in the list and select the new 3CX Windows App