AWS - connect to PostgreSQL from Python not working

Sorry to bother you, but I have been struggling to use Python to connect to the AWS PostgreSQL database based on this instruction https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/UsingWithRDS.IAMDBAuth.Connecting.Python.html, as it always displays timeout error.

I have also set up a config file in ~/.aws folder to configure the boto3, with the following:

[default] 
aws_access_key_id = X
aws_secret_access_key = X

import os
import boto3
import psycopg2

ENDPOINT="url"
PORT="5432"
USR="kaggle"
REGION="us-east-2a"
os.environ['LIBMYSQL_ENABLE_CLEARTEXT_PLUGIN'] = '1'

session = boto3.Session(profile_name='default')
client = boto3.client('rds',region_name=REGION)

token = client.generate_db_auth_token(DBHostname=ENDPOINT, Port=PORT, DBUsername=USR, Region=REGION)

try:
    conn = psycopg2.connect(host=ENDPOINT, port=PORT, user=USR, password=token)
    cur = conn.cursor()
    cur.execute("""SELECT now()""")
    query_results = cur.fetchall()
    print(query_results)
except Exception as e:
    print("Database connection failed due to {}".format(e))

The error is:

Database connection failed due to could not connect to server: Connection timed out (0x0000274C/10060)
    Is the server running on host "url" (IP) and accepting
    TCP/IP connections on port 5432?

It appears your scenario is:

• An Amazon RDS database in a VPC with Publicly Accessible = Yes
• Your own computer on the Internet (outside of AWS)
• You want to connect to Amazon RDS from your computer

Things to check:

• Amazon RDS has been launched in a public subnet (defined as a subnet with a Route Table entry that points to an Internet Gateway)
• You are using the DNS Name of the RDS database to connect (as provided in the RDS console)
• A Security Group on the RDS database that permits inbound access on port 5432 to your computer's public IP address, or to 0.0.0.0/0 (but that is bad from a security perspective)