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/765/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-fda6b9c8-b8e7-49f4-b27f-eb04e469f036",
      "cw-f3dd8c84-fa71-4c3f-876e-0e078140237e"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0528c0f1-2454-46a8-a266-5460e3cf21f7",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/765/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f3dd8c84-fa71-4c3f-876e-0e078140237e"
  }
}