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/maps1/29957/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-614348cf-d4a6-4a7f-866f-4fe88808ec13",
      "cw-91426c81-0dba-4cd5-bf14-2770bcb43299"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-a44bf026-c2f4-4a3b-9fe8-1c0131fe1874",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/29957/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-91426c81-0dba-4cd5-bf14-2770bcb43299"
  }
}