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/maps1/10637/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-d5e59583-8273-4298-b138-0aee188be15a",
      "cw-4237b290-d4f9-4203-ad06-54f374928030"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-05adacc1-46f3-4b96-8a6d-6e6052297d77",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/10637/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-4237b290-d4f9-4203-ad06-54f374928030"
  }
}