Domestic and foreign currencies are converted into RMB for cash purchase. What does the bank earn?
Exchange domestic foreign currency for RMB, and buy cash, that is, exchange foreign currency for RMB. The money earned by the bank must be the money of the foreign currency party. This bank was originally engaged in currency business. You buy RMB in foreign currency cash, in which RMB is a commodity sold by the bank, so foreign currency is of course earned.