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/859/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-303fc4ad-865b-457a-921a-17100b4040f3",
      "cw-e3610233-1791-4f80-875d-463c36241282"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-9a0b882c-4f6a-49f6-8b3d-275a260609d2",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/859/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-e3610233-1791-4f80-875d-463c36241282"
  }
}