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/maps1/2276/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-561a3dca-5c88-4911-97d0-f9480c9f3e6b",
      "cw-64d77158-b2cb-4d3f-bb61-0bae5bd584c5"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e4f44a57-ca30-4ad4-bed2-1a5ea8d593c7",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/2276/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-64d77158-b2cb-4d3f-bb61-0bae5bd584c5"
  }
}