The lot size is the minimal amount of currency available for buying or selling.
For each market there is an established lot size on Bequant. For example, the BTC lot size is equal to 0.01 BTC.
The most common issue is when you attempt to buy/sell a certain amount of assets where the desired quantity is less than the lot size.
There are two options to address this:
You can withdraw these assets or just store them on your account.
You can buy more coins of this currency specifying the exact price.