Cannot import mesh to planning scene in rviz using python

Question

I am using Ros Noetic Ninjemys with Ubuntu 20.04. I am trying to import a mesh into the scene using python. I am able to import the STL file of the mesh using the rviz gui, but I am not able to do the same using python. The code is given below.

#! /usr/bin/env python3

import sys
import copy
import rospy
import moveit_commander
import moveit_msgs.msg
import geometry_msgs.msg
from tf.transformations import quaternion_from_euler

from math import pi, tau, dist, fabs, cos

from std_msgs.msg import String
from moveit_commander.conversions import pose_to_list

def all_close(goal,actual, tolerance):
    if type(goal) is list:
        for index in range(len(goal)):
            if abs(actual[index]-goal[index]) > tolerance:
                return False
    elif type(goal) is geometry_msgs.msg.PoseStamped:
        return all_close(goal.pose, actual.pose, tolerance)

    elif type(goal) is geometry_msgs.msg.PoseStamped:
        return all_close(goal.pose, actual.pose, tolerance)

    elif type(goal) is geometry_msgs.msg.Pose:
        x0, y0, z0, qx0, qy0, qz0, qw0 = pose_to_list(actual)
        x1, y1, z1, qx1, qy1, qz1, qw1 = pose_to_list(goal)
        # Euclidean distance
        d = dist((x1, y1, z1), (x0, y0, z0))
        # phi = angle between orientations
        cos_phi_half = fabs(qx0 * qx1 + qy0 * qy1 + qz0 * qz1 + qw0 * qw1)
        return d <= tolerance and cos_phi_half >= cos(tolerance / 2.0)

    return True

class MoveGroupPythonInterfaceTutorial(object):
    def __init__(self):

        super(MoveGroupPythonInterfaceTutorial, self).__init__()
        moveit_commander.roscpp_initialize(sys.argv)
        rospy.init_node("motion_plan_2", anonymous = True)

        self.robot = moveit_commander.RobotCommander()

        self.scene = moveit_commander.PlanningSceneInterface()

        rospy.sleep(2)

        p = geometry_msgs.msg.PoseStamped()
        p.header.frame_id = self.robot.get_planning_frame()
        p.pose.position.x = 0.30
        p.pose.position.y = 0
        p.pose.position.z = 0
        filename =  "./assembly.STL"
        self.scene.add_mesh("assembly", p, filename)
        
        group_name = "arm"
        self.move_group = moveit_commander.MoveGroupCommander(group_name)

        self.display_trajectory_publisher = rospy.Publisher(
            "/move_group/display_planned_path",
            moveit_msgs.msg.DisplayTrajectory,
            queue_size =20,
        )

        self.planning_frame = self.move_group.get_planning_frame()
        print("Planning frame: %s" % self.planning_frame)

        self.eef_link = self.move_group.get_end_effector_link()
        print(" end effector link =: %s" % self.eef_link)

        self.group_names = self.robot.get_group_names()
        print("Available planning Groups:", self.robot.get_group_names())

        print("the robot state is: ")
        print(self.robot.get_current_state())
        print("")

    def go_to_joint_state(self):
        
        joint_goal= self.move_group.get_current_joint_values()
        joint_goal[6]= -3.11

        self.move_group.go(joint_goal, wait = True)

        self.move_group.stop()
        
        joint_goal[6] = 3.11
        self.move_group.go(joint_goal, wait=True)
        self.move_group.stop()

        current_joints = self.move_group.get_current_joint_values()
        return all_close(joint_goal ,current_joints, 0.01)
    
    def go_to_pose_goal(self, px,py,pz,ox,oy,oz,ow):
        
        pose_goal = geometry_msgs.msg.Pose()
        pose_goal.position.x = px
        pose_goal.position.y = py
        pose_goal.position.z = pz
        pose_goal.orientation.x = ox
        pose_goal.orientation.y = oy
        pose_goal.orientation.z = oz
        pose_goal.orientation.w = ow
    
        self.move_group.set_pose_target(pose_goal)
        
        success = self.move_group.go(wait = True)

        self.move_group.stop()

        self.move_group.clear_pose_targets()

        current_pose = self.move_group.get_current_pose().pose
        return all_close(pose_goal,current_pose, 0.01)
    
    def cartesian_path(self, scale=1):
        waypoints = []

        wpose=self.move_group.get_current_pose().pose
        wpose.position.x += scale*0.1
        waypoints.append(copy.deepcopy(wpose))

        (plan,fraction) = self.move_group.compute_cartesian_path(waypoints, 0.01,0.0)

        self.move_group.execute(plan, wait = True)  
    
def main():
    try:

        input("press enter to start the program")
        tutorial = MoveGroupPythonInterfaceTutorial()

        input("enter the orientation")
        q = quaternion_from_euler(0,1.5707,0)
        
        tutorial.go_to_pose_goal(0.25,0.25,0.25,q[0],q[1],q[2],q[3])
        print("the robot has moved to the desired location")
        print(q)

        input(" the tool is moving to zero position")
        tutorial.go_to_joint_state()
        print("the tool is in zero position")
        
        print("moving to forward 10 cm")
        tutorial.cartesian_path()
        print("movement complelte. exiting")

    except rospy.ROSInterruptException:
        return
    except KeyboardInterrupt:
        return
    
if __name__ =="__main__":
    main()

When I try to import the mesh I get the following error.

I tried changing the location of the STL file, changing the extenstion to "stl", and tried using a different STL file.