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/656/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-3f7441d3-40d4-41b7-8f19-3a15bf40eb8e",
      "cw-51514861-c9c7-4cf0-928a-1c9da5f22d74"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-44e6f99e-e8f8-4993-bddd-8df99f72453f",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/656/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-51514861-c9c7-4cf0-928a-1c9da5f22d74"
  }
}