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/maps1/3762/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-91e4d04b-5bfe-41e5-ba9a-4261b54c1d0b",
      "cw-5c375881-f9d9-450c-bec3-53405e781d5f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-03ff2cfb-75de-4742-ba54-5fe44547d9aa",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/3762/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-5c375881-f9d9-450c-bec3-53405e781d5f"
  }
}