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/1177/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-de551022-6703-4470-a6ae-68bc7c0d1918",
      "cw-db31f896-1b70-4580-940d-15112c3f2197"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-89ca6317-d534-436d-9876-1dfd97e30170",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1177/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-db31f896-1b70-4580-940d-15112c3f2197"
  }
}