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/maps1/12338/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-435de84a-773b-4ebc-90e3-958b46df7b8b",
      "cw-bf234452-8d5d-425f-bc7d-6d2ad550833f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0b967f9f-5642-4c4c-b2a5-505a25753883",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/12338/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-bf234452-8d5d-425f-bc7d-6d2ad550833f"
  }
}