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/maps1/8926/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-885560cb-c373-4a81-8445-60a1b3690486",
      "cw-6da48d0b-437e-4005-8a41-a83e39582626"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0e89677d-6554-4a10-af0a-3defeb183099",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/8926/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6da48d0b-437e-4005-8a41-a83e39582626"
  }
}