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/maps1/6750/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-0888ef80-3c11-44ac-9025-7b2bd5b93db5",
      "cw-afb984e7-2a8d-4756-b934-e7713b6e42e3"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-bf8e128d-d180-4564-9f9f-94635c9a5771",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/6750/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-afb984e7-2a8d-4756-b934-e7713b6e42e3"
  }
}