Mode S beast multilat not supported?

I am currently feeding flightaware with this setup and it says my receiver is not supported. Any ideas?
I am a GS with planeplotter and have multilat all setup there.

Same here. MLAT does not work with PP feeds. You have to run PiAware.

Correct. The planeplotter multilateration system is completely separate from the FlightAware multilateration system; they work differently and do not exchange data.