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/maps1/6256/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-a3b09a2f-396e-4a29-9613-bc23d47ad0ef",
      "cw-e70196a1-c09a-4907-ae20-e59065693cad"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-eada37fb-f21f-41fb-b883-12f314da8d2d",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/6256/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-e70196a1-c09a-4907-ae20-e59065693cad"
  }
}