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/maps1/23013/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-f180c708-e477-4007-94b1-ad6cc5b95890",
      "cw-75bb7412-6996-44d0-b297-0721d2b77242"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-d5de9d03-ddc9-4040-bce5-37701b138917",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/23013/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-75bb7412-6996-44d0-b297-0721d2b77242"
  }
}