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/maps1/9591/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-e86dd01a-26af-4ec4-85cb-727322f904d4",
      "cw-1c01a414-ef83-4a9e-9dca-81ce1fabf202"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-28002ecf-87ec-4adc-96b1-26277502ec23",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/9591/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-1c01a414-ef83-4a9e-9dca-81ce1fabf202"
  }
}