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/maps1/8907/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-68c65183-0893-4217-a076-1c49ae65e3b6",
      "cw-f9a95d5b-9aca-454d-bb27-f2d1bf53d25a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-54f93c0e-ad32-4d08-858f-c09817667573",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/8907/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f9a95d5b-9aca-454d-bb27-f2d1bf53d25a"
  }
}