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/999/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-2beb4a9d-eaa7-47d0-8498-68e0b8badcf8",
      "cw-0ebdd2a5-f696-4760-b1d1-6a4aaba86c01"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e15f3569-23c7-4f55-ac28-c51f5a0dfa9b",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/999/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-0ebdd2a5-f696-4760-b1d1-6a4aaba86c01"
  }
}