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/633/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-9b2ed773-0058-4fe6-8e23-05c80f9ccf6c",
      "cw-25da135c-2a3e-45fd-8760-abeca3ea0665"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-4d3ae6af-3987-4692-9f70-1bcc4301a7c9",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/633/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-25da135c-2a3e-45fd-8760-abeca3ea0665"
  }
}