AWS Update table not working

I'm uisng updateTable of DynmaoDB and I'm passing the following params object:

{
    "TableName": "movies",
    "AttributeDefinitions": [{
            "AttributeName": "subtitle",
            "AttributeType": "S"
        }],
    "GlobalSecondaryIndexUpdates": [{
            "Create": {
                "IndexName": "subtitle",
                "ProvisionedThroughput": {
                    "ReadCapacityUnits": "5",
                    "WriteCapacityUnits": "5"
                },
                "KeySchema": [{
                        "AttributeName": "subtitle",
                        "KeyType": "HASH"
                    }],
                "Projection": {
                    "ProjectionType": "ALL"
                }
            }
        }],
    "ProvisionedThroughput": {
        "ReadCapacityUnits": "5",
        "WriteCapacityUnits": "5"
    }
}

but it gives me the following error:

• UnexpectedParameter: Unexpected key 'AttributeDefinitions' found in params


• UnexpectedParameter: Unexpected key 'Create' found in params.GlobalSecondaryIndexUpdates[0]]

But based on the the documentation I need to pass them?! So why is it giving me this error?

Thanks