curl --request POST \
  --url http://localhost:8080/cabinet/admin/users/{user_id}/promo-group \
  --header 'Content-Type: application/json' \
  --data '
{
  "promo_group_id": 123
}
'

{
  "success": true,
  "message": "<string>",
  "old_promo_group_id": 123,
  "new_promo_group_id": 123,
  "promo_group_name": "<string>"
}