Amazon web services 描述流程未知操作异常

您能帮我解释一下为什么我会收到以下DynamodB流请求的UnknownOperationException：

POST https://dynamodb.eu-west-1.amazonaws.com/
Authorization: AWS4-HMAC-SHA256 Credential=...,SignedHeaders=host;x-amz-content-sha256;x-amz-date;x-amz-target,Signature=...
Content-Length: 100
Content-Type: application/x-amz-json-1.0
X-Amz-Date: 20151105T093459Z
X-Amz-Target: DynamoDBStreams_20120810.DescribeStream
x-amz-content-sha256: ...
{"StreamArn":"arn:aws:dynamodb:eu-west-1:147720290114:table/TestSav/stream/2015-11-04T09:47:27.834"}

但是，相同流ARN的awscli命令成功：

aws --debug dynamodbstreams describe-stream --stream-arn "arn:aws:dynamodb:eu-west-1:147720290114:table/TestSav/stream/2015-11-04T09:47:27.834"

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请求应该发送到streams.dynamodb…com而不是

dynamodb…com