Because forward foreign exchange transactions involve the risk of exchange rate changes. For example, Company A handles forward foreign exchange transactions in Bank B, and both parties agree to exchange a certain currency at a certain price X in the future. When the contract was signed, Bank B immediately hedged its business with overseas competitors. Suppose that Company A finds that the ratio of the current exchange rate to the forward price is inappropriate after the expiration and chooses to default, Bank B must perform the transaction with the overseas market-making bank, and Bank B will face losses, usually the difference between the forward price and the current price, which is generally less than 5% (unless there is extreme exchange rate change). In order to prevent this kind of risk, usually Bank B will ask Company A to deposit 3%-5% of the deposit, or give Company A a credit. If there is exchange rate loss, it will be paid directly through credit to turn the loss into a loan to Company A. ..