Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://digital.libraries.psu.edu/iiif/info/maps1/6581/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-cf2b100f-1cc4-4f50-b7c8-06da8448a4e2",
      "cw-61535df8-2a4b-4f20-85b9-d0990d35625d"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-efc88020-5747-4dfc-9ce1-fdd4788201c1",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/6581/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-61535df8-2a4b-4f20-85b9-d0990d35625d"
  }
}