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/maps1/12222/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-d878f9e3-e522-4fdd-9573-c6a25f2886ba",
      "cw-7bf57f96-be58-4de1-ac08-6027d1427f71"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e3d040a0-83c0-4156-9d6e-33ba2901dc6c",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/12222/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-7bf57f96-be58-4de1-ac08-6027d1427f71"
  }
}