Hi, I barely have enough experience, that I doubt I could be dangerous... . Most of my experience was telling engineers to get it done.
Check your connection methods. I do believe Modbus RTU is a serial protocol, and would not support any IP addresses for communications. Typically it would be RS485 or RS232.
Don't confuse it with ModBus TCP which would be caried over an addressable network.
Hostely, to debug, I would post your question to a good LLM like ChatGPT 4.0. This might help you down the path to discovery.