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/maps1/23055/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-d416c7dd-45f6-4671-a5ac-60ab542563e3",
      "cw-61486476-bb77-4779-8a83-1d93f9583706"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-d7324a79-fc15-4802-95cd-6da9846e1958",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/23055/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-61486476-bb77-4779-8a83-1d93f9583706"
  }
}