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/maps1/2056/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-0e358173-922e-4378-96f3-4698bcb09388",
      "cw-0878c01b-d541-4069-8f86-1fbad258f526"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-68aacaea-49e3-4841-9244-74e66ca1d8b2",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/2056/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-0878c01b-d541-4069-8f86-1fbad258f526"
  }
}