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/849/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-31821bab-c259-4cb3-8fd4-749a5588cadf",
      "cw-86ffe55a-952c-4454-adfe-24b5db6790ec"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-db7425e5-0efa-4d7b-a0c6-2e846ffd22f9",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/849/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-86ffe55a-952c-4454-adfe-24b5db6790ec"
  }
}