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/maps1/8714/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-e282c230-137a-4094-86eb-96281800e1af",
      "cw-a068bfd0-57cb-45e4-90fa-6b068635576a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-fce0c166-a240-4b6a-9b74-9191ce4bbde2",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/8714/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a068bfd0-57cb-45e4-90fa-6b068635576a"
  }
}