Foreign exchange transactions are actually not aimed at a certain currency, but at the exchange rate composed of two currencies. This is an index investment, and you can go short and long at the same time. For example, if you buy an English commodity "GBPUSD", your purchase behavior can actually be decomposed into "buying pounds and selling dollars"; So, you can sell it without buying it. When you sell GBPUSD, your investment behavior can actually be decomposed into "selling pounds and buying dollars". In foreign exchange transactions, buying and selling are irrelevant. Selling can't be paid by settlement, and the settlement of purchase and sale orders uses "liquidation" instruction.