Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/903/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-14d34402-ef1e-4368-9648-475b5b2f5568",
      "cw-f34fdd09-23c5-44b8-bc5f-e7d11f28f35b"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-6604fa56-8122-4eda-9f6f-c88bdde87182",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/903/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f34fdd09-23c5-44b8-bc5f-e7d11f28f35b"
  }
}