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/748/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-890a321f-d31d-46f0-91cc-73e14169f968",
      "cw-60195bb7-9103-4f3c-acf5-9538e958c16f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ae36e0ec-1597-4490-98f4-55cde42a378b",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/748/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-60195bb7-9103-4f3c-acf5-9538e958c16f"
  }
}