How to get DJI MSDK (v5) RTK location and fused Alti?

Question

I want to get RTK info in Kotlin. I have a Fragment, where i define:

val RTKInf = RTKLocation()                            // RTK and fused
val RTKSts = RTKSystemState()                         // see if connected

Now, in OncreateView, I do:

var altFus   : Double? = 0.00
RTKCenter.getInstance().addRTKLocationInfoListener {

            if(it != null && it.rtkLocation != null) altFus = it.rtkLocation.getMobileStationLocation().getAltitude()

        }

But the value of Altfus is always zero.

I can netiehr find a documented or an undocumented flightControllerKey that might correspond to RTK.

Please help.