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/maps1/9857/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-7034d86e-b5ee-414e-a193-73b0499acaaf",
      "cw-2b1cfa99-c719-4a44-b34f-b0eca8999a2b"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-63108bc2-fa9d-4022-9307-9cdd0eebc721",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/9857/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-2b1cfa99-c719-4a44-b34f-b0eca8999a2b"
  }
}