SteamMasterID неправильный. Ну или ты не с основы пишешь.
Also notice that you can trade only with your friends, and people with known trade link. If you're trying to initiate Bot->Master trade, such as !loot, then you need to either have SteamMasterID on Bot's friendlist, or SteamTradeToken of SteamMasterID set in Bot's config. Make sure that the token is valid - otherwise, you won't be able to send a trade.
https://github.com/JustArchi/ArchiSteamFarm/wiki/FAQ