Nose Wheel Steering Configuration

I am having trouble getting Arduplane 3.8 to control the nose wheel steering.

Steering works OK manually, but not in FBWA or Auto modes.

The plane is a Phantom FX-61 with elevens, no rudder, fitted with an undercarriage.

The steering channel is 7. RC7_FUNCTION is set to 26 which is ground steering.

Other parameters are as follows.

GROUND_STEER_ALT = 5m.

GROUND_STEER_DPS = 90 deg/s.

STEER2SRV_P = 4.03 m.

STEER2SRV_I = 0.1.

STEER2SRV_D = 0.02.

STEER2SRV_IMAX = 1500 cdeg.

STEER2SRV_MINSPD = 1 m/s.

STEER2SRV_TCONST = 0.5 s.

STEER2SRV_DRTSPD = 0 (derating is disabled)

In FBWA or Auto modes, I expect the nose wheel to turn left (or right) if I yaw the plane right (or left) so it holds a straight course. Instead, the nose wheel does not turn automatically at all. Only manual control turns the nose wheel. Can anyone advise me what I have not done correctly?