Template:Networking install Modbus serial RutOS
From Teltonika Networks Wiki
Installation
From FW version of RUT9_R_00.07.05 and newer Modbus Serial Client package is installed by default. To install it on older FW versions open device's WebUI, navigate to Services → Package manager → Packages and search for Modbus Serial Master and press + icon to install. After installation you should see a status Installed on this package.