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/maps1/13260/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-c7e9fa4f-e125-4008-b494-ef532bf4f4ec",
      "cw-dc534cde-e253-4ca8-b1fe-d5057fa7f2dd"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-dca60874-fb67-4799-bc00-d24a027e48ca",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/13260/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-dc534cde-e253-4ca8-b1fe-d5057fa7f2dd"
  }
}