unexpected 400 bad request response

Hi,

I'm attempting  a POST Request using SoapUI 5.3.0 but keep getting a 400 Bad Request response.

The annoying thing is, is that the exact same request works in a different API testing tool. Same Endpoint and resource.

The following headers are supplied in both SoapUI and other API Testing tool:

Content-Type: application/json
Accept: application/json

Below is the request body:

{
  "ProcessingStartTime": "2017-12-12T08:44:33.7437679+00:00",
  "ProcessingEndTime": "2017-12-12T08:47:06.2027702+00:00",
  "IssuesCommonData": {
    "ClaimId": "00000",
    "CwClaimId": "fgsfdgs546456",
    "ClientClaimId": "gfhgf546456",
    "FacilityCwId": 1,
    "CeCwId": 1,
    "PayorBucket": "Commercial",
    "DateOfService": "2017-01-02T00:00:00",
    "DischargeDate": "2017-10-09T00:00:00",
    "BillType": "131",
    "CwClaimVersion": 1,
    "Mrn": null,
    "CwDept": "fdssgsdfs"
  },
  "Issues": [
    {
      "Id": "fggfdfg433tdfg43",
      "IssueTypeName": "test",
      "IssueTypeId": 5,
      "IssueId": "fgs5464hhgfh",
      "InstanceId": "fgs5464hhgfh",
      "IssueCategory": "fgdfgdhfdgdg",
      "Description": "test",
      "Impact": 0.0,
      "GrossImpact": 10.0,
      "ActualImpact": null,
      "CmsPercentage": null,
      "CwClientPercentage": null,
      "CwDept": "dgdg",
      "DateCreated": "2017-07-13T13:29:56.277Z",
      "HcpcsCode": "fgdg",
      "Modifiers": "",
      "RevenueCode": "gdgfgdf",
      "PrimaryDiagCode": "4535ggfdg",
      "IssueData": {},
      "ExclusionTypeId": null
    }
  ],
  "CwClaimId": "fgsfdg563546",
  "CwClaimVersion": 1
}

In SoapUI I get the following response:

HTTP/1.1 400 Bad Request
Cache-Control: no-cache
Content-Length: 127
Content-Type: application/json; charset=utf-8
Expires: -1
Access-Control-Allow-Origin: *
Date: Tue, 12 Dec 2017 14:35:28 GMT

{
  "message": "The request is invalid.",
  "modelState": {
    "claimDto": [
      "An error has occurred."
    ]
  }
}

In the other API Testing Tool using the exact same details I get a 200 OK.

Can someone shed some light on this. Is there a setting in SoapUI I need to change?

Thanks.