JointPositionController in Ignition has a bug in topic name?

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I am using Ignition Gazebo Citadel and ROS2 Foxy to control a bipedal robots. To control its joints, I tried to use JointPositionController. However, it did not work when I start the node using the JointPositionControlller. It says that it include the number in topic name, which is illegal.

In default setting, JointPositionControlller has index number of axis as a part of the topic name. (plz check out this:)

But, the topic name cannot begin with a number (plz check this as well)

Is this bug? If anyone successfully used JointPositionController in Ignition Gazebo, please let me know how you write the topic name in the node.

Thanks