Mirador viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1021/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b92d9972-b2f8-4e7f-ae6f-5e00318aab86",
      "cw-90849b8a-d2c6-4d93-a3e9-6393b070300e"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-175e8458-47c1-42fb-9da7-5a34a3bdfe01",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1021/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-90849b8a-d2c6-4d93-a3e9-6393b070300e"
  }
}