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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://collections.ubcic.bc.ca/iiif/2/17720/manifest",
    "isFetching": false
  },
  "window": {
    "autoScrollAnnotationList": true,
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-0e516131-4e29-4046-b256-10ad0a1a8312",
      "cw-0df8c4b4-041f-4f09-9848-116ff03da269"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-a28e2303-f08f-4edf-a472-fa3371aa1589",
    "manifestId": "https://collections.ubcic.bc.ca/iiif/2/17720/manifest",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-0df8c4b4-041f-4f09-9848-116ff03da269",
    "loadedManifest": "https://collections.ubcic.bc.ca/iiif/2/17720/manifest"
  }
}