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/747/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-049b1a33-af90-428b-83fa-ff7b7fd561f9",
      "cw-87aca4e6-1ece-4a9d-a7bc-b8f6556bb262"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f3f7fb96-b1ac-455f-9070-7c7e12fee23d",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/747/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-87aca4e6-1ece-4a9d-a7bc-b8f6556bb262"
  }
}