mbusd

mbusd is an open-source Modbus TCP to Modbus RTU (RS-232/485) gateway. It presents a network of RTU servers as single TCP server.

That is a TCP-Server, which acts as a RTU-Client to get data from Modbus RTU-Server devices.

When you add the Sunsynk HASS repository, it includes a mbusd addon called "Modbus TCP to Modbus RTU Gateway Add-on".