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/maps1/28139/manifest.json",
    "isFetching": false
  },
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    "highlightAllAnnotations": false,
    "id": "window-5e8a9d9b-1ea4-4bbb-89f1-c949961bc492",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/28139/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-1c923e95-dfce-45d9-a5be-b63d0a02a631"
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