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/maps1/28250/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-531bef8f-553d-4b77-873a-428ef10ce631",
      "cw-0a803573-222e-4917-a1e4-92a6f31de508"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-de720a85-f978-4929-b7a3-a97832baef45",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/28250/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-0a803573-222e-4917-a1e4-92a6f31de508"
  }
}