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/maps1/11791/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-dcc2b4d8-6464-4bbe-9ee5-642ccdb9a1ea",
      "cw-cc391329-ce91-4f55-8cb8-2ba8738b2494"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-3c8bc7eb-85ce-427b-9ab7-617d5ac96fdd",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/11791/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-cc391329-ce91-4f55-8cb8-2ba8738b2494"
  }
}