Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
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    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://digital.libraries.psu.edu/iiif/info/maps1/21977/manifest.json",
    "isFetching": false
  },
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    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-5b03fdd6-cf7b-405d-b7c9-42e3904e39a2",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/21977/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
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