AWS Lambda job to backup RDS instances

lambda.py

import boto3
import datetime

def lambda_handler(event, context):
    print("Connecting to RDS")
    client = boto3.client('rds')
    
    print("RDS snapshot backups stated at %s...\n" % datetime.datetime.now())
    client.create_db_snapshot(
        DBInstanceIdentifier='web-platform-slave', 
        DBSnapshotIdentifier='web-platform-%s' % datetime.datetime.now().strftime("%y-%m-%d-%H"),
        Tags=[
            {
                'Key': 'CostCenter',
                'Value': 'web'
            },
        ]
    )
    
    for snapshot in client.describe_db_snapshots(DBInstanceIdentifier='web-platform-slave', MaxRecords=50)['DBSnapshots']:
        if create_ts < datetime.datetime.now() - datetime.timedelta(days=7):
            print "Deleting snapshot id:", snapshot['DBSnapshotIdentifier']
            client.delete_db_snapshot(
                DBSnapshotIdentifier=snapshot['DBSnapshotIdentifier']
            )

I am using the same code but getting below error -

{ "errorMessage": "An error occurred (InvalidParameterValue) when calling the CreateDBSnapshot operation: The specified instance is a member of a cluster and a snapshot cannot be created directly. Please use the CreateDBClusterSnapshot API instead.", "errorType": "ClientError", "stackTrace": [ [ "/var/task/lambda_function.py", 19, "lambda_handler", "'Value': 'NIRDS'" ], [ "/var/runtime/botocore/client.py", 312, "_api_call", "return self._make_api_call(operation_name, kwargs)" ], [ "/var/runtime/botocore/client.py", 605, "_make_api_call", "raise error_class(parsed_response, operation_name)" ] ] }