USDt is the Settlement Coin. Thalex, in its sole discretion, can select a different Settlement Coin.
Unsettled P&L, either realized or unrealized, is not available for withdrawal. Settlement credits / debits the Settlement Coin balance with the Unsettled P&L. This process uses a market-based USDt/USD rate to convert P&L, which is USD-denominated, into a USDt amount.
Participants should ensure they have sufficient balance in the Settlement Coin.