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/710/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-2f1415e5-db55-4fc9-8b8f-a7ab3c8a4272",
      "cw-fd1d8ee2-b8a8-4168-b75a-b8ef1f8ae4d6"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-a400740e-bd8a-4c88-b3f5-e1657bdec43f",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/710/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-fd1d8ee2-b8a8-4168-b75a-b8ef1f8ae4d6"
  }
}