The right of defense to perform at the same time means that the parties bear debts to each other, and if there is no sequence of performance, it shall be performed at the same time  One party has the right to refuse its request for performance before the performance of the other party
One party shall have the right to refuse its corresponding request for performance if the other party's performance of the debt is not in conformity with the agreement
A buys a car from B, and B will not deliver the car until A has not paid the price.