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/964/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-0bb33101-afdc-4b39-8600-33e8230b8e92",
      "cw-776c0769-03a0-418f-ad91-30295ad3b18a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-9d824142-da05-4f56-a535-1eb054a43dbd",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/964/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-776c0769-03a0-418f-ad91-30295ad3b18a"
  }
}