Send Patch request through Rest API in powershell and TFS2015 - powershell

Question

Please find below request body I created in powershell with Patch method to create a bug in TFS. But not able to create a bug and gettign message that "TF401320: Rule Error for field Found In. Error code: Required, HasValues, InvalidEmpty.","typeName"..... I also attached error code here.
# Base64-encodes the Personal Access Token (PAT) appropriately
$base64AuthInfo = [Convert]::ToBase64String([Text.Encoding]::ASCII.GetBytes(("{0}:{1}" -f $user,$pass)))
function CreateJsonBody
{
$value = #"
[
{
"op": "add",
"path": "/fields/System.Title",
"value": "TestBug"
},
{
"op": "add",
"path": "/fields/Microsoft.VSTS.TCM.ReproSteps",
"value": "Our authorization logic needs to allow for users"
},
{
"op": "add",
"path": "/fields/Microsoft.VSTS.Common.Priority",
"value": "1"
},
{
"op": "add",
"path": "/fields/Microsoft.VSTS.Common.Severity",
"value": "2 - High"
}
]
"#
return $value
}
$json = CreateJsonBody
$uri = "http://xxx-xxxxx-006:8080/tfs/xxx/xxxxx/_apis/wit/workItems/"+"$"+"bug/?api-version=2.0"
Write-Host $uri
$result = Invoke-RestMethod -Uri $uri -Method Patch -Body $json -Credential
$credential -ContentType "application/json-patch+json" -Headers #{Authorization=("Basic {0}" -f $base64AuthInfo)}
But not getting response.
Below error is getting
{
"$id": "1",
"innerException": null,
"message": "TF401320: Rule Error for field Found In. Error code: Required, HasValues, InvalidEmpty.",
"typeName": "Microsoft.TeamFoundation.WorkItemTracking.Server.RuleValidationException, Microsoft.TeamFoundation.WorkItemTracking.Server, Version=14.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",
"typeKey": "RuleValidationException",
"errorCode": 600171,
"eventId": 3200
}
Please help me. I already write code to create bugs for another account but not able to do here.