Add the logging switch to the command line. This is typically “/l*v logfile.txt” but you would have to confirm with the installer. Then review the log file.
Try to manually install it but with out the silent switch.
To quote the Avaya documentation on performing a Silent install of their client …
“You can install Avaya one-X Agent through an automated package distribution tool that makes use of the Microsoft Windows Installer service. The Avaya one-X Agent installer packages contain the MSI Installer. To pass custom (user-defined) properties to the MSI installer, you must extract the MSI installer image from the Avaya base package installers.”
Sounds like you can’t use the EXE installer with the Silent option, you need to extract the MSI installer and use it directly.