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/maps1/10859/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-383845e6-ace2-4bff-a992-eeece029c953",
      "cw-01fdbeb6-c4c8-4e02-8c89-4ed2e5c93c7d"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-044c6621-6341-40ab-8bd2-c8399fb2c4fb",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/10859/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-01fdbeb6-c4c8-4e02-8c89-4ed2e5c93c7d"
  }
}