Fees are charged in the Settlement currency of the contract (so a USDT fee for ETHUSDT, and a XBT fee for XBTUSD for example). In Multi Asset Margin mode, if you don’t have enough of the Settlement currency in your account, we will take from your other Margin currencies to cover the fee.
Funding fees are also paid in the settlement currency for a contract. Similar to trading fees, when funding fees are taken from your account, if you do not have sufficient available Settlement currency, then other Margin currencies will be taken from your margin and converted into the settlement currency to cover the funding fee.
In the same way, when you realise a loss, if you have insufficient Settlement currency to cover it, we will take the required amount from your other Margin currencies.
In all of the cases above, you will see a spot conversion transaction in your transaction history that converts your existing margin currency into the required amount of Settlement currency. These conversions will occur at the index prices with haircuts applied.