You will need to deposit enough to pay for the initial margin of a trade. Let’s say you trade on BTC/USD with 30x leverage. The minimum quantity is 0.01 BTC.
The initial margin calculation
(1 x Quantity) / Leverage + Spread
Let’s say BTCUSD is $8,020 (Buy Price) and $8,000 (Sell Price).
(1 x 0.01) / 30 + 20 = $20.00033 or 0.0025 BTC
That would be your minimum BTC to open this trade.