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/699/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-7ee3fe30-1fc3-452a-95c7-462a06185f75",
      "cw-b4d79777-a3fe-4a2b-bc40-123ca66d5367"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-7dd2b978-eee1-4e48-8bee-b6f3bd69d7ba",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/699/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-b4d79777-a3fe-4a2b-bc40-123ca66d5367"
  }
}