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/712/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-bdea18f4-6677-48a6-a97d-63939815af9f",
      "cw-f66c2d05-a48e-484e-9e99-55dc7eca4126"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-23c0e875-7658-422e-9c7c-2794c3643176",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/712/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f66c2d05-a48e-484e-9e99-55dc7eca4126"
  }
}