Initial Margin is the minimum balance required from your account to open a trade.
On the other hand, Free Margin, also known as "Usable Margin" is the amount available in your account to be used for opening more trades. It is also the amount that allows you to move against the market movement before reaching a margin or liquidation call. It is equivalent to the difference between Equity and Total Used Margin.
Variation Margin is the unrealized profit (or loss) on open positions or transactions.
Your Total Margin requirement is simply the sum of these two amounts, and you must maintain at least this amount in your Axi account at all times.