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/maps1/11837/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-fa1a6bf1-3582-4c73-9f54-af33ea8c1557",
      "cw-091aed66-9d4c-4a58-b597-24c835748ebf"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e1a980ed-f05c-49da-9690-087d94834ceb",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/11837/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-091aed66-9d4c-4a58-b597-24c835748ebf"
  }
}