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/maps1/9427/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-a932e2ac-e471-455a-9ff7-30c72fba755d",
      "cw-55339c6c-cdb2-4b80-8cdc-7190fe187207"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-8b4d460f-930a-408b-aab1-1891a55b195a",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/9427/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-55339c6c-cdb2-4b80-8cdc-7190fe187207"
  }
}