You are paying for the right to buy bitcoin at the strike price on the expiration date.
You need USD in your account to purchase options. You can send USD to LedgerX via wire transfer or sell bitcoin on the platform for USD. See Fund Your Account.
BTC Mini Quantity: the number of contracts you want to buy. Minimum quantity = 1.
1 long call option mini contracts gives you the right to buy 0.01 BTC at the strike price on the expiration date.
Limit Price: the price you pay for the call option. Options prices are quoted in terms of 1 bitcoin.
Total Premium Paid: the total dollar amount you pay the seller at time of trade