Credit cards should have a fixed limit of 30. There are two reasons for this:

The first reason is that if the reserved limit is too low, you must increase the amount of credit card swipes every month. This leads to requirements for equipment, which also increases the number of swipes for each card, and also causes the repayment to be repaid immediately, which makes it easier to risk;

Second The reason is that when the reserved amount is sufficient, no matter whether there is a shortage of money or not, there will be enough funds to alleviate the problem and avoid the risk of not paying back the loan.