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/1086/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-757a5ae3-45ff-4d5a-be0f-9ce35b7822b1",
      "cw-6a39799e-db3c-4587-9f24-ec9775f53321"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-64a70c35-b0b5-4fff-8aa0-58b02814537c",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1086/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6a39799e-db3c-4587-9f24-ec9775f53321"
  }
}