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/maps1/6572/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-9bd1d7ed-81bc-43d0-9038-0602e58f133a",
      "cw-8155005a-3b52-47fd-9d68-e97e7bdf9ce3"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ecfc9c90-8bf0-4344-8b4e-70e3a86841fc",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/6572/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-8155005a-3b52-47fd-9d68-e97e7bdf9ce3"
  }
}