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/maps1/23969/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-a6517fc5-fff4-47a2-97b5-3afd3004295b",
      "cw-7af0697d-cfcc-4dbe-8706-86e4f6dddc7f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-de6707bf-dad4-415c-b958-460773bd8271",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/23969/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-7af0697d-cfcc-4dbe-8706-86e4f6dddc7f"
  }
}