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/640/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-86548deb-f243-410c-9b26-9372fe21c1d3",
      "cw-b446f0c9-de0d-4d93-83bb-0269044975bc"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-7590c7f5-8417-448b-814a-56318f8804e5",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/640/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-b446f0c9-de0d-4d93-83bb-0269044975bc"
  }
}