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/maps1/18602/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-e95b0cb5-88fd-440d-8933-4f85ec201ced",
      "cw-1bc1fe0e-d16d-4768-80ba-a92399ed95ec"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-37aa3555-3b91-418c-a202-9524696c4456",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/18602/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-1bc1fe0e-d16d-4768-80ba-a92399ed95ec"
  }
}