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/maps1/9810/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-a1fc146d-a703-4569-a656-b69fdcd9c37d",
      "cw-f8badb83-b7e3-49d6-94cc-4e946f7a0937"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-99dfee4c-fe8d-48ab-bf1d-72b821a16dea",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/9810/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f8badb83-b7e3-49d6-94cc-4e946f7a0937"
  }
}