curl --request PUT \
  --url https://api.hubapi.com/feature-flags/v3/{appId}/flags/{flagName}/portals/{portalId} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{}'

{
  "appId": 123,
  "flagName": "<string>",
  "portalId": 123
}