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/maps1/18819/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-5114e61c-d42f-46a8-b989-b92ffee8cde1",
      "cw-a8b0ad75-f919-450b-92b2-0fd28ceaac58"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-c95fccc9-db7a-4522-a152-56f96f1df14d",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/18819/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a8b0ad75-f919-450b-92b2-0fd28ceaac58"
  }
}