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/603/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-4b300048-1ee4-4d14-8955-1c6a8aee202d",
      "cw-0e631d52-8d8d-4895-8d57-205c2eb51c9c"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ba0653f6-6d26-40c6-877f-fed9a91ae034",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/603/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-0e631d52-8d8d-4895-8d57-205c2eb51c9c"
  }
}