Peter wants to find out if Sapphira was part of her husband’s deceit. The amount which is in question is thus the amount that Ananias gave to the church. In asking this question Peter gives Sapphira a chance to repent and come clean by saying that it is less than the price which they received.
8 And Peter said to her, “Tell me whether you sold the land for so much.” And she said, “Yes, for so much.”