Limit Grid feed-in with SMA

Setup is a Multiplus II-GX, Sunny Box 3, MPPT RS.
I like to be ready when the day comes we have to pay for feeding into the grid.

When I set the option “Limit system feed-in” to zero, the MPPT RS goes to zero W, but the Sunny Boy is still feed into the grid.

I’m already using Node-Red. What is my next option? Setting the Multiplus to inverter only so there will be a frequency shift?

Thanks.