Get data from /api/MetricService/Metrics

I have installed the OpenManage Enterprise server, and use it to manage one physical server with iDRAC9 Enterprise Perpetual License .

I have installed the power Manage plugin on  the "Console and Plugins" page ,and I have download a OpenManage Enterprise Advanced Trial License for iDRAC9 form dell.com and I have imported the OpenManage Enterprise Advanced license to the physical server.

I found the api '/api/MetricService/Metrics' in dell-openmanage-enterprise_reference-guide, and I want to try it.

But it return error. The error message : 

{
"error": {
"code": "Base.1.0.GeneralError",
"message": "A general error has occurred. See ExtendedInfo for more information.",
"@Message.ExtendedInfo": [{
"MessageId": "CMET0003",
"RelatedProperties": [],
"Message": "Unable to complete the operation because the interface of the Plugin Application is not registered.",
"MessageArgs": [],
"Severity": "Warning",
"Resolution": "Register the PluginApplication and retry the operation. For information about registering aPlugin Interface, see the User's Guide of the respective Pluginavailable on the support site."
}]
}
}

Howt to reslove it? Any suggestions? Thanks