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/maps1/27424/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-6e24f70c-046d-4436-8f9c-084fe45f6f5c",
      "cw-4d98ac90-6983-4e56-8a15-bdb05189ab82"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-2c8288fd-0ab1-4e47-9216-e5593fb51de6",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/27424/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-4d98ac90-6983-4e56-8a15-bdb05189ab82"
  }
}