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/maps1/26419/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ae2ea538-6a3b-415d-bdbe-1d796670f2e4",
      "cw-5c2689d6-f995-4619-820e-027cee474a1c"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-2c6bcfb6-5eba-4452-84ab-9769ed8bd855",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/26419/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-5c2689d6-f995-4619-820e-027cee474a1c"
  }
}