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/906/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ea29fb76-413f-4bdb-acb3-1e74636ad893",
      "cw-c3b4cd88-d151-4c06-9981-a64d3758d8b0"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0d84fee5-216b-4fb4-996b-d9a80dd866ba",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/906/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-c3b4cd88-d151-4c06-9981-a64d3758d8b0"
  }
}