AWS OpenSearch Serverless创建索引遇403访问拒绝求助

我正在搭建AWS OpenSearch Serverless的最小可用示例，编写了如下Python代码：

import boto3
from opensearchpy import OpenSearch, RequestsHttpConnection, AWSV4SignerAuth

host = 'onb565zzbfkjr3spn8v5.us-east-1.aoss.amazonaws.com'
region = 'us-east-1'

credentials = boto3.Session().get_credentials()
auth = AWSV4SignerAuth(credentials, region)
client = OpenSearch(
    hosts = [{
        'host': host,
        'port': 443
    }],
    http_auth = auth,
    use_ssl = True,
    verify_certs=True,
    connection_class = RequestsHttpConnection
)

def create_index(index_name):
    index_body = {
      'settings': {
        'index': {
          'number_of_shards': 1
        }
      }
    }
    response = client.indices.create(index_name, body=index_body)
    print('\nCreating index:')
    print(response)

create_index('myindex')

已执行以下操作：

• 创建了拥有AmazonOpenSearchServiceFullAccess、AmazonESFullAccess权限的IAM用户，还添加了两个内联策略：
  策略1：

  {
      "Version": "2012-10-17",
      "Statement": [
          {
              "Sid": "VisualEditor0",
              "Effect": "Allow",
              "Action": "aoss:APIAccessAll",
              "Resource": "*"
          }
      ]
  }
  

  策略2：

  {
      "Version": "2012-10-17",
      "Statement": [
          {
              "Sid": "VisualEditor0",
              "Effect": "Allow",
              "Action": "aoss:DashboardsAccessAll",
              "Resource": "*"
          }
      ]
  }
  

  （创建集合时未显示后两项权限）
• 执行aws configure配置密钥和区域
• 创建了设置为Public访问、指定该IAM用户为主体且开启全部访问权限的集合

尽管完成上述操作，创建索引时仍返回403（Access denied）错误，请问我遗漏了什么？

更新：已在AWS社区提交相同问题。

内容的提问来源于stack exchange，提问作者AlwaysLearning