Koala Wallet has default settings that work for the vast majority of transactions you make. Unfortunately there are some edge cases where the default may not work. If you're trying to send ETH to an exchange and all your transactions are failing, we have the solution below.
Instead of a normal Ethereum address, some exchanges may instead use a smart contract as their deposit address. Transactions to such contracts require a higher gas limit than Koala Wallet's default. Checking failed transactions on the block explorer will show that they failed due to being out of gas.
Don't worry, the solution is simple. When sending ETH to those services, expand the Advanced Settings menu and set the Gas limit to 50000. There is no need to change the "Nonce" setting.
This should be enough for sending ETH to any exchange smart contract address. When sending Ethereum tokens like USDT, the gas limit is set higher by default, so there should be no need for any changes. You can read more about Ethereum's advanced settings here.