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/751/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-0c4ef50c-8668-42dc-9935-5d2e86a6e1d3",
      "cw-64493c01-f469-466f-8381-e253f35e260b"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-c4f955a9-b64b-467e-960d-d6ac81ea09f2",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/751/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-64493c01-f469-466f-8381-e253f35e260b"
  }
}