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/maps1/27756/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-80b27a44-5577-46c4-8d74-ec40326cff41",
      "cw-8a7e1074-0a59-4ddc-8674-59dd3d31fcad"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-749717f3-6e20-42f1-b190-5905c242c4c7",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/27756/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-8a7e1074-0a59-4ddc-8674-59dd3d31fcad"
  }
}