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/maps1/5982/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-7ccb8470-cf79-49fc-a5bc-1c482992e81d",
      "cw-97547bd8-eeaf-41a5-b7b8-a2adaef4d0f9"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b6e9e3c3-3e60-4380-a3e5-006423f778af",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/5982/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-97547bd8-eeaf-41a5-b7b8-a2adaef4d0f9"
  }
}