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/maps1/17935/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-90173ac5-f2d1-4c49-b43a-adcd238404b0",
      "cw-57211e0e-7a12-4643-be27-e5b87951e779"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ed5bde8d-98a5-4e24-b0c9-fd5d57444720",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/17935/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-57211e0e-7a12-4643-be27-e5b87951e779"
  }
}