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/maps1/7433/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-770cc1c1-72ba-4299-9540-0f263b989d24",
      "cw-e504c590-d501-4d40-baf8-344d08728bd4"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-73f8a32c-3c1f-4e82-a1b8-adee140dc704",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/7433/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-e504c590-d501-4d40-baf8-344d08728bd4"
  }
}