If a trader places a limit order, current limit orders freeze a margin in an account to enable their execution. This is done so that the order book is not clogged with fake orders, i.e. orders that cannot be actually fulfilled by a trader. The lot size is 100 futures contracts. The minimum contract is 0.01 lot without any swaps.
A margin for buy trades is calculated in a special way, bearing in mind the highest risk. For instance, opening a sell position at 0.2000, a trader is running a risk that InstaFutures will be closed at 0.9999 in case his forecast comes wrong. In other words, he will lose 100 * 0.1 * (0.9999 - 0.2000) ~ $8 per every 0.1 lot open.
Therefore, to sell 0.1 lot at 0.2000, the margin will be $8. To reduce risks, the trading platform will require 150% of a margin size to open a position. In the example above, a trader will be required to provide the following margin: $8 * 150% = 12$.
A basic margin for buy positions will be calculated as follows: 100 * trade size in lots * market quote.