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/660/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-5a08b56d-6318-4f0a-8148-6666f2f70853",
      "cw-2b80629d-fc01-4430-9ba7-85cbf9928dd6"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-2d6beedc-6c90-4717-ad0b-74c70b313123",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/660/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-2b80629d-fc01-4430-9ba7-85cbf9928dd6"
  }
}