No available vehicle found in Yard Monitor (lyrdm)

Hi,

I am new in WM. I made some configuration based on configuration guide. I try to create vehicle in lyrdm and check-in the vehicle and made movement in lychp. When I back to t-code, lyrdm, I choose one outbound delivery and right click mouse with assign vehicle. The system shows "No available vehicle found". However, the same vehicle can be assigned to inbound delivery.

Is there anyone can give me some advice?

Many thanks for your help,

Jessie.