Cannot get ContactSensorCfg to work

[QuackBeans]

I'm trying to add contact sensors to my robot env before i clone it for training, however every time i get the following error: "Sensor at path '/World/envs/env_.*/Robot/base_link' could not find any bodies with contact reporter API."

I have enabled activate_contact_sensors in my robot's ArticulationCfg but nothing changes. Perhaps im missing something.

Here is my robot config and my scene setup function from within my env class

LIMBO_CFG = ArticulationCfg(
    spawn=sim_utils.UsdFileCfg(
        usd_path=_LIMBO_USD_PATH,
        # This is crucial for the thigh contact penalty to work.
        activate_contact_sensors=True,

        # These are robust default physics properties, similar to the spdrbot example.
        # They are a great starting point and can be tuned later if needed.
        rigid_props=sim_utils.RigidBodyPropertiesCfg(
            rigid_body_enabled=True,
            max_linear_velocity=1000.0,
            max_angular_velocity=1000.0,
            max_depenetration_velocity=100.0,
            enable_gyroscopic_forces=True,
        ),
        articulation_props=sim_utils.ArticulationRootPropertiesCfg(
            enabled_self_collisions=False,  # Usually disabled for performance
            solver_position_iteration_count=8,
            solver_velocity_iteration_count=1,
        ),
        collision_props=sim_utils.CollisionPropertiesCfg(
            collision_enabled=True,
        ),
    ),

    def _setup_scene(self):
        self.robot = Articulation(self.cfg.robot)
        spawn_ground_plane(prim_path="/World/ground", cfg=GroundPlaneCfg())
        
        cfg_cuboid = sim_utils.CuboidCfg(
            size=(0.1, 0.1, 0.1),
            rigid_props=sim_utils.RigidBodyPropertiesCfg(),
            mass_props=sim_utils.MassPropertiesCfg(mass=1.0),
            collision_props=sim_utils.CollisionPropertiesCfg(),
            visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(1.0, 0.0, 0.0)),
        )

        cfg_cuboid.func(
            "/World/envs/env_.*/RedBox",
            cfg_cuboid,
            translation=(0.0, -20.0, 1.0)
        )
        
        contact_sensor_cfg = ContactSensorCfg(
            prim_path="/World/envs/env_.*/Robot/base_link",
            update_period=0.0,
            track_air_time=False,
        )
        self.contact_sensor = ContactSensor(contact_sensor_cfg)

        # Clone multiple envs (amount specified in cfg)
        self.scene.clone_environments(copy_from_source=False)
        self.scene.articulations["robot"] = self.robot
        self.scene.sensors["contact_sensor"] = self.contact_sensor

I have also tried the following prim path for the contact sensor:
prim_path="/World/envs/env_.*/Robot",

What am i missing here?