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/maps1/23498/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-f5e9b73c-39c3-4466-8345-f372b3f7fdde",
      "cw-82fa66fa-a07f-44f1-9dba-22218df7a2dc"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-c4ad0ee0-2a6d-4ffa-b45b-8dfe7a7ead4e",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/23498/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-82fa66fa-a07f-44f1-9dba-22218df7a2dc"
  }
}