Send Warning Message to OSD

Hello

I am using a F405 FC running Arduplane connected to a Raspi. Communication over pymavlink (heartbeat, mode change,…) are working. The camera/video OSD is configured and working, also the warning messages are shown (e.g. low battery). How do I send a message from raspi to the FC which then appears on the OSD as message? I tried like this (also varying the type of SEVERETY):

ap.mav.statustext_send(mavutil.mavlink.MAV_SEVERITY_WARNING,b"test")

Nothing is shown on the OSD. Any ideas?

No ideas? Some pointers would be helpful

Can you try this Complete Parameter List — Copter documentation