Whenever using the XRAY JSON endpoint and passing the Test Plan Key the Tests are not being added to the test plan

http://localhost:21000/rest/raven/1.0/import/execution

{
 "testExecutionKey": "CALC-1983",
 "info" : {
 "summary" : "Execution of automated tests for release v1.3",
 "description" : "This execution is automatically created when importing execution results from an external source",
 "user" : "admin",
 "revision" : "1.0.42134",
 "startDate" : "2014-08-30T11:47:35+01:00",
 "finishDate" : "2014-08-30T11:53:00+01:00",
 "testPlanKey" : "CALC-1982"
 },
 "tests" : [
 {
 "testKey" : "CALC-1985",
 "start" : "2014-08-30T11:47:35+01:00",
 "finish" : "2014-08-30T11:50:56+01:00",
 "comment" : "Successful execution",
 "status" : "PASS"
 }
 ]
}