Sorry I don't know python, but why is your SL negative? This is how I modify a trade to use a trailing stop

{
    "command": "tradeTransaction",
    "arguments": {
        "tradeTransInfo": {
            "cmd": 1,
            "order": xxx,
            "symbol": "GBPUSD",
            "type": 3,
            "volume": 0.2,
            "price": 1.29954,
            "sl": 1.29707,
            "offset": 15
        }
    }
}