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/maps1/3705/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-c6a56469-60ac-4707-8370-6cb4e335d4bd",
      "cw-7c0fa754-cc01-4222-aed9-40451dc77b28"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-65eea395-427a-44f2-b823-2d0ec788a980",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/3705/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-7c0fa754-cc01-4222-aed9-40451dc77b28"
  }
}