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/598/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ae849216-ad4e-48a3-9bc5-c81b2fc67548",
      "cw-a5e09206-c19a-4c08-bfbf-d015156cfe23"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-14bd7db6-6e3e-4e6a-93a9-c521fa4023aa",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/598/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a5e09206-c19a-4c08-bfbf-d015156cfe23"
  }
}