Golang create instance failed

ecsClient, err := ecs.NewClientWithOptions("cn-hangzhou", config, credential)

........

// create instance
createRequest := requests.NewCommonRequest()
createRequest.Method = "POST"
createRequest.Domain = "ecs.aliyuncs.com"
createRequest.Version = "2014-05-26"
createRequest.ApiName = "CreateInstance"
// ecs.t1.xsmall  ecs.t1.small  ecs.s2.small ecs.s1.small
createRequest.QueryParams["InstanceType"] = "ecs.g5.large"
createRequest.QueryParams["ImageId"] = "centos_7_04_64_20G_alibase_201701015.vhd"
createRequest.QueryParams["RegionId"] = "cn-hangzhou"
createRequest.QueryParams["InstanceName"] = "AliAPICreate"
createRequest.QueryParams["HostName"] = "Elan"
//createRequest.QueryParams["SecurityGroupId"] = "None"
createRequest.QueryParams["SystemDisk.Size"] = "40" // GB
createRequest.QueryParams["SystemDisk.Category"] = "cloud"

if response, err := ecsClient.ProcessCommonRequest(createRequest); err != nil {
 log.Println(errHandle(err))
} else {
 fmt.Print(response.GetHttpContentString())
}