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/maps1/24251/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-3e4f51d2-ab04-4553-8f8e-6ffe361bfe57",
      "cw-559bd1ce-9482-45fa-8929-a57be2d399aa"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-845b98db-f954-4a77-9010-d15cef8cf876",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/24251/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-559bd1ce-9482-45fa-8929-a57be2d399aa"
  }
}