当通过Lambda调用时，CloudFormation脚本会失败。

【以下的问题经过翻译处理】 我在S3上有一个CloudFormation堆栈文件，从控制台启动它时可以很好地工作。但是，当我使用AWS Lambda中的boto3触发相同的脚本时，我会得到一个编码错误消息。解码后，我得到以下JSON输出。（为了可读性，已转换为YAML）

---
allowed: false
explicitDeny: false
matchedStatements:
  items: []
failures:
  items: []
context:
  principal:
    id: AROA3H7OMTCQKOORZGNNY:Spawn-reward-service
    arn: arn:aws:sts::773057xxxxxx:assumed-role/Spawn-reward-service-role-g0vgzj5h/Spawn-reward-service
  action: ec2:RequestSpotFleet
  resource: arn:aws:ec2:us-east-1:773057xxxxxx:subnet/subnet-e18921ca
  conditions:
    items:
    - key: ec2:Vpc
      values:
        items:
        - value: arn:aws:ec2:us-east-1:773057xxxxxx:vpc/vpc-aa2884c1
    - key: aws:Resource
      values:
        items:
        - value: subnet/subnet-e18921ca
    - key: aws:Account
      values:
        items:
        - value: '773057xxxxxx'
    - key: ec2:AvailabilityZone
      values:
        items:
        - value: us-east-1e
    - key: ec2:ResourceTag/Name
      values:
        items:
        - value: 1e subnet
    - key: ec2:SubnetID
      values:
        items:
        - value: subnet-e18921ca
    - key: aws:Region
      values:
        items:
        - value: us-east-1
    - key: aws:Service
      values:
        items:
        - value: ec2
    - key: aws:Type
      values:
        items:
        - value: subnet
    - key: 773057xxxxxx:Name
      values:
        items:
        - value: 1e subnet
    - key: ec2:Region
      values:
        items:
        - value: us-east-1
    - key: aws:ARN
      values:
        items:
        - value: arn:aws:ec2:us-east-1:773057xxxxxx:subnet/subnet-e18921ca

Lambda角色包含以下策略：AmazonEC2SpotFleetTaggingRole, NetworkAdministrator and AWSCloudFormationFullAccess。不确定具体在哪里卡住了。
完整的lambda函数请参考：
import json, boto3

def lambda_handler(event, context):
    cloudformation = boto3.client('cloudformation')
    response = cloudformation.create_stack(
        StackName='yj',
        TemplateURL='https://s3.amazonaws.com/cf-templates-xxxxxxxxxxxx-us-east-1/reward-service-01-spot.yaml',
        Parameters=[
            {
                'ParameterKey': 'InstanceType',
                'ParameterValue': 't2.large'
            }
        ]
    )
    return response