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/645/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b5497077-2499-43af-8e13-be0f271f4cbb",
      "cw-e9a340ba-4d22-4e5c-abc0-fb240f3831be"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-6626993e-9d15-4f78-b295-5ec04199b9d9",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/645/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-e9a340ba-4d22-4e5c-abc0-fb240f3831be"
  }
}