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/maps1/6052/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ccaa5049-2cdb-4ea9-9097-b6acf3762bdc",
      "cw-c7afa320-ba98-4020-8009-d5f9d14571e3"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-94307fa6-44e6-480e-b52b-3dc354bf2a35",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/6052/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-c7afa320-ba98-4020-8009-d5f9d14571e3"
  }
}