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/617/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-171332c6-2d88-4ffd-b6cc-e8b0f83140ee",
      "cw-cdf7a8c8-3e6c-426f-9739-e2923da8d2fc"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f4c6bf8e-52c2-47d2-905b-2f370842110b",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/617/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-cdf7a8c8-3e6c-426f-9739-e2923da8d2fc"
  }
}