使用 Boto3 访问另一个账户中的 S3 存储桶时，Lambda 超时

我正在尝试使用 boto3 从我的 AWS Lambda 访问另一个账户中的 S3 存储桶.以下是我配置的步骤.:
1. 在我的 Lambda 所在的账户 A 中，我创建了执行角色 (Lambda-S3-SNS-VPC-Role) 并将一个 AmazonS3FullAccess 托管策略和一个内联策略附加到它:

I am trying to access S3 bucket in another account from my AWS Lambda using boto3. Below are the steps I configured.:
1. In Account A where my Lambda is I create Execution role (Lambda-S3-SNS-VPC-Role) and attach to it one AmazonS3FullAccess Managed Policy and one Inline policy as:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Stmt1489133353000",
            "Effect": "Allow",
            "Action": [
                "sts:AssumeRole"
            ],
            "Resource": [
                "arn:aws:iam::<Account-B-ID>:role/access-s3-bucket-from-lambda-in-another-acc-role"
            ]
        }
    ]
}

在我的 S3 存储桶所在的账户-B 中，我创建了一个 IAM 角色(access-s3-bucket-from-lambda-in-another-acc-role)，如下所示:- 附加 AmazonS3FullAccess 托管策略和信任关系:

In Account-B, where my S3 bucket is present, I created one IAM Role (access-s3-bucket-from-lambda-in-another-acc-role) as below: - Attached AmazonS3FullAccess managed policy and in Trust Relationship :

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::<Account-A-ID>:role/Lambda-S3-SNS-VPC-Role",
        "Service": "lambda.amazonaws.com"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}

此外，在账户 B 的 S3 存储桶中，给出了以下存储桶策略

Also, in S3 Bucket in account B, gave below bucket policy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::<Account-A-ID>:role/Lambda-S3-SNS-VPC-Role"
            },
            "Action": "s3:*",
            "Resource": [
                "arn:aws:s3:::my-bucket-in-acc-B",
                "arn:aws:s3:::my-bucket-in-acc-B/*"
            ]
        }
    ]
}

以下是我的 Lambda 函数代码:

Below is my Lambda Function code:

def lambda_handler(event, context):
    sts_connection = boto3.client('sts')

    acct_b = sts_connection.assume_role(
        RoleArn="arn:aws:iam::<Account-B-ID>:role/access-s3-bucket-from-lambda-in-another-acc-role",
        RoleSessionName="cross_acct_lambda"
    )
    print('acct_b: ',acct_b)

但是在测试时，什么也没有发生，函数超时了.请指导.

But while testing, nothing is happening and the Function gets timed out. Please guide.