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/634/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-820dda8b-bc63-4d17-a9f2-eb07eb6cd3ff",
      "cw-7438b5e2-d67d-46b1-a571-83e117b45dbe"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-7063d9f9-2ae3-4f02-8ffe-4e19a0e4c403",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/634/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-7438b5e2-d67d-46b1-a571-83e117b45dbe"
  }
}