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/maps1/22976/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-f0a3cbe6-4cc6-49cd-b986-ab3e0e4ddbe9",
      "cw-6580097d-8a4a-4490-9821-59a8a28de6b7"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b1d672a1-5d99-4c04-ba45-4a8aa9f47402",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/22976/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6580097d-8a4a-4490-9821-59a8a28de6b7"
  }
}