Do you have the correct addresses for the slave/unit and the coil/resgister?
Sorry but I can’t help you further. My solar inverter does not have any coil registers. I did try using HA modbus platform but decided that I wanted more control over debugging and Modbus polling rates, so I use Node-Red.
I can only suggest setting up Node-Red (either as an HA add-on or on something else like a Raspberry Pi) and setting up a connection and modbus-getter node. https://community.home-assistant.io/t/modbus-tcp-which-hardware/441823 You can then easily test that the Modbus TCP connection works and then check that you have the right slave/coil address. Error messages in Node-Red are easily visible and quite informative for failed read/write attempts. That would, I think, only leave you with HA yaml configuration as the issue.