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/maps1/6364/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-f5bf2928-c28c-44a9-a995-4bc542f3a8d1",
      "cw-1ae1b938-8e9b-4fdd-9300-336b978726ab"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-63f1398f-c53f-49e0-85c8-f6ae531f64d3",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/6364/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-1ae1b938-8e9b-4fdd-9300-336b978726ab"
  }
}