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/659/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-5b802099-8fa7-4a51-ad34-6c1daa02e8eb",
      "cw-b0145064-a5c2-4262-b578-3a87d8b498b2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-61914972-1f2c-4815-b5cf-de110cc54d84",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/659/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-b0145064-a5c2-4262-b578-3a87d8b498b2"
  }
}