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/780/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-9af913d6-b29d-4f4f-8eda-498942622ac5",
      "cw-5be5e8eb-74e3-487e-bbad-53e55848db9a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ed024fb0-6f16-4ead-876a-e666e8462aa3",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/780/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-5be5e8eb-74e3-487e-bbad-53e55848db9a"
  }
}