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/1121/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-34ce1462-e4b7-446a-a430-b9024ec59bfb",
      "cw-9fe2348a-3997-4395-887f-c036b3565544"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-2a59b783-f1bb-4c85-83b1-c388ccb924f5",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1121/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-9fe2348a-3997-4395-887f-c036b3565544"
  }
}