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/909/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-0e6672ad-d23c-4a68-a2b5-693d0f64e25c",
      "cw-6e077f82-bc2a-4c10-a9af-77dfd767aeb1"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f33b9588-9ca0-416b-9b69-b4a164fdaff8",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/909/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6e077f82-bc2a-4c10-a9af-77dfd767aeb1"
  }
}