Modbustcp MaxFeedInPower not writable

Hi, I am using threephase multiplus 2 with Fronius inverter.


When I put on the slider in Cerbo GX menu [ Limit system Feed-in] manually the system throttles to zero feed-in and works like a charm.
Now I want to automate this with Nodered so when prices are negativ, it should not feed-in.
I can read /Settings/CGwacx/MaxFeedInpower in Node red and get the data.
But when I try to write the same data back, nothings happens. The slider does not change. Look that the register is not writetable. Can someone look in to it please.

It is writeable with the W/ path and I can change the [Max feed in W] field, but not the slider [ Limit system feed-in] Does someone know which register thats is ?