Another learning experience for those out there configuring a duet 3, with beta firmware, when you do this M584 X0.0 Y0.1 Z0.2:0.3 E0.4:0.5 you end up controlling z motors when you try to retract/extrude lol BUT when you do:
M584 X0.0 Y0.1 Z0.2:0.3
M584 E0.4:0.5
Then retracting/extruding ends up using the right motors.
Now.... the last piece of the puzzle is the BLtouch and then setup mesh bed leveling. It does successfully self test a couple times when powered on, then led stays solid red and duet web interface shows "0" for z probe. When I try to do M401 then nothing.. if I'm using a duet 3 what governs "pin" or "servo" number in the below? (M950 S# or M280 P#) I'm running out of trouble shooting strategies.. 
config.g
; Z-Probe
M558 P9 C"io2.in" H5 R1 F50 T6000 A5 S0.02 B1 ; set Z probe type to bltouch and the dive height + speeds
M950 S0 C"io2.out"
G31 P500 X1 Y2 Z2.5 ; set Z probe trigger value, offset and trigger height
M557 X15:440 Y15:440 P20 ; define mesh grid
deployprobe.g
M950 S0 C"io2.out"
M280 P0 S10
retractprobe.g
M950 S0 C"io2.out"
M280 P0 S90
Pin connections...
Red 5v to 5v EXT
Yellow/orange, signal to io2.out
2 grnd wires to GRND
White, Zmin to io2.in