API to Create link to EWM's WorkItem from ETM's TestCase

Hi All,
I am trying to link between a testcase and workitem using REST/OSLC API.
Using the OSLC API, I am able to create the link by making a GET request to testcase and the link tag <oslc_qm:testsChangerequest rdf:resource="xxxxxxxxxxxx" /> to the rdf response and make a PUT call to the same testcase url usign the modified body and it is successfully creating the link.
But when GC is enabled for the ETM project, I am not getting the CCM links as tags in the testcase's response and even if I try adding the tag and make the PUT call the link is not showing up.
I have also tried the following rest api.
Endpoint : {{serverUrl}}/qm/service/com.ibm.rqm.defects.service.internal.rest.ICmIntegrationRestService/newPlanItemLinks?webContext.projectArea=_1Qw9ATYJEfCytIdIQjexgA
Body :
testArtifactItemId:_ADt3UTYMEfCytIdIQjexgA
workItemJsonStrings:{"uri":"https://devalm:9443/ccm/resource/itemName/com.ibm.team.workitem.WorkItem/123","summary":"123: Test workitem from Java."}
gcConfigValue:https://devalm:9443/gc/configuration/11
rqmProjectAreaItemId:_1Qw9ATYJEfCytIdIQjexgA
projectAreaItemId:_1Qw9ATYJEfCytIdIQjexgA
Headers :
Accept:text/json
Content-Type:application/x-www-form-urlencoded
Response :
{
"soapenv:Body": {
"response": {
"returnValue": {
"_eQualifiedClassName": "http:///com/ibm/team/core/services.ecore:NullDataArg",
"type": "NULL"
},
"method": "postNewPlanItemLinks",
"_eQualifiedClassName": "http:///com/ibm/team/core/services.ecore:Response",
"interface": "com.ibm.rqm.defects.service.internal.rest.ICmIntegrationRestService"
},
"_eQualifiedClassName": "http://schemas.xmlsoap.org/soap/envelope/:Body"
},
"_eQualifiedClassName": "http://schemas.xmlsoap.org/soap/envelope/:Envelope"
}
Please let me know what I am missing or if there is any other way to achieve this.
Thanks and Regards,
Krishna K.