Why E_PHYSICSBEGINCONTACT2D event is not trigger for rigidBody?

Below is Not working
SubscribeToEvent(mainRigidBody, E_PHYSICSBEGINCONTACT2D, URHO3D_HANDLER(Urho2DConstraints, HandleBallContactStart));

But this is working:
SubscribeToEvent(mainPhysicslWorld, E_PHYSICSBEGINCONTACT2D, URHO3D_HANDLER(Urho2DConstraints, HandleBallContactStart));

Why E_PHYSICSBEGINCONTACT2D event is not trigger for rigidBody?

Because E_PHYSICS* events are send from the physics world by design.
Nodes send E_NODE* events.

Thanks, and it is work now