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/652/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-accfc62d-bcca-4fda-9062-480a97288851",
      "cw-38ae1f2d-80a7-4b1a-9da6-55e0a1bb318f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-c0436816-482f-4125-a307-5f3bedf27441",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/652/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-38ae1f2d-80a7-4b1a-9da6-55e0a1bb318f"
  }
}