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/maps1/23371/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-deec73e3-ce5f-4cce-8c4a-c87d73749253",
      "cw-35ba01ea-f05e-4139-a974-328483bfe8db"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ab40107d-d675-48e3-9253-e8fe0bfdf04b",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/23371/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-35ba01ea-f05e-4139-a974-328483bfe8db"
  }
}