Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/134455/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-4bfa88c5-4982-4592-a78b-a2779576606d",
      "cw-b7230447-d6f8-402e-aad2-9b99ae279ce6"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b7e2a5a7-054d-4bb2-9e26-65a4e88f8bb2",
    "manifestId": "/api/digital_items/134455/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-b7230447-d6f8-402e-aad2-9b99ae279ce6",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/134455/2/manifest.json/",
    "canvasIndex": 0
  }
}