So maybe the error you are getting is because you are trying to set the Inverter directly instead of through the Data Manager ? Im not sure but from what i understand when you have the Data Manager in your setup .. that acts as a bridge for the Communication with the Inverter ... (or many Inverters in case of big solar parks)
See this Document about the SMA Modbus Interface of the SMA Data manager (link)
It has its own Modbus Registers for setting power limitation.
If you manage to get some information from someone qualified let us know,
im also interested how this can be tied with Node-red.
