MethodNotImplemented: 501 Received http2 header with status: 404

I have deployed triton docker container in vertex ai and here is my code to send request to vertex ai using python aiplatform_v1.
Code:
```
import numpy as np
import json
import time
import cv2
import os
import base64
import matplotlib.pyplot as plt
from google.cloud import aiplatform_v1
import traceback
from google.api.httpbody_pb2 import HttpBody

project = "my-project-name"
location = "location"
endpoint_id = "endpoint-id"

endpoint_name = f"projects/{project}/locations/{location}/endpoints/{endpoint_id}"

client = aiplatform_v1.PredictionServiceClient()

s_path = "/input-images-folder-path/"
s_data = os.listdir(s_path)

input_data = [cv2.imread(os.path.join(s_path,s_data[0]))]
pred_time = []
print("Start Time:",time.time())
for image_name in s_data:

if image_name.split(".")[-1]!="txt":

try:
input_data = [cv2.imread(os.path.join(s_path,image_name))]
b64_data = []
for img in input_data:
content = str(base64.b64encode(cv2.imencode('.png', img)[1].tobytes()).decode("utf-8"))
b64_data.append(content)

b64_data = np.array(b64_data, dtype=object)

payload = {
"id": "0",
"inputs": [
{
"name": "input_image",
"shape": [1,1],
"datatype": "BYTES",
"parameters": {},
"data": b64_data.tolist(),
}
],
}

# Convert payload to bytes
payload_inst = json.dumps(payload).encode("utf-8")
http_body = HttpBody(content_type="application/octet-stream", data= payload_inst)

request = aiplatform_v1.RawPredictRequest(endpoint = endpoint_name, http_body = http_body)

start = time.time()
print("start prediction.........")
response = client.raw_predict(request=request, timeout=30) # Timeout in seconds
print("end prediction.........")
end = time.time()
pred_time.append(end-start)

except Exception as e:
print(traceback.print_exc())
print(e)
print('====================================================================================================')

print("End Time:",time.time())
print("Average Time:",sum(pred_time)/len(pred_time))
```
Running above code i got "501 Received http2 header with status: 404" error.
Error shows that endpoint is not found but i followed official documentation.

Can someone tell me what's wrong in code?