Starting from 1.16:
Firstly look at player, then press "Trade" button("v" by default), and request will be sent. Then, second player must do the same.
You can also use /trade 'player_name' command
Config file (config/trade.properties)
trade_swap_time_second - time to wait before items sawpping
request_time_second - request lifetime
unlimited_trade - allows to trade on any distance, from different dimensions
If you have issues/ideas