RRbot velocity controllers in ros2_control

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I am a newbie in ros2_control manager. I had followed the demo and tutorial explanation on the position controllers, and everything is working fine. Yet, when I wanna switch the controller to velocity controller, the arm could not work properly when I trying to send the command as

ros2 topic pub /forward_velocity_controller/commands std_msgs/msg/Float64MultiArray "data:
- 0.5
- 0.5"

The arm is not moving at all. I had tried to configure the velocity controller, and switch the controller from position to velocity controller. Yet, it is not working.

Note: The URDF that I am using is rrbot_system_multi_interface.

Can anyone guide me on this?

Thanks.