Upload Document with Text Anchors - 500 error

I'm receiving a 500 error when I upload a document to /packages with the following roles and approvals. Any idea where the error could be coming from? Here's the request detail:

POST https://sandbox.esignlive.com/api/packages

------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="file"; filename="eSignLive - test -- 2017-03-23 07_38pm.pdf"

%PDF-1.4 ....  (rest of file removed)


------WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="payload"

{
  "name": "Please sign this document",
  "type": "PACKAGE",
  "status": "SENT",
  "roles": [
    {
      "id": "signer1",
      "type": "SIGNER",
      "signers": [
        {
          "lastName": "test",
          "firstName": "test",
          "email": "[email protected]"
        }
      ]
    }
  ],
  "documents": [
    {
      "name": "eSignLive - test -- 2017-03-23 07_41pm.pdf",
      "index": 0,
      "id": "document1",
      "extract": true,
      "approvals": [
        {
          "role": "signer1",
          "fields": [
            {
              "type": "SIGNATURE",
              "width": 250,
              "height": 50,
              "extract": true,
              "extractAnchor": {
                "text": "[signature1]",
                "anchorPoint": "BOTTOMRIGHT",
                "index": 0,
                "width": 250,
                "height": 50,
                "leftOffset": 0,
                "topOffset": 0
              }
            }
          ]
        }
      ]
    }
  ]
}

------WebKitFormBoundary7MA4YWxkTrZu0gW--

Response: {"messageKey":"error.internal.default","message":"Unexpected error. We apologize for any inconvenience this may have caused you, please try again. If the problem persists, please contact our support team.","code":500,"name":"Unhandled Server Error"}