Contradiction with Genesis 23:16-18
This verse states that Abraham bought the field from Ephron in the presence of witnesses, affirming the legitimacy of the transaction rather than indicating any contradiction.
Genesis 23:16-18: And Abraham hearkened unto Ephron; and Abraham weighed to Ephron the silver, which he had named in the audience of the sons of Heth, four hundred shekels of silver, current [money] with the merchant.
Contradiction with Acts 7:16
This verse states that Abraham bought the sepulcher from the sons of Hamor in Shechem, rather than the field of Machpelah in Hebron.
Acts 7:16: And were carried over into Sychem, and laid in the sepulchre that Abraham bought for a sum of money of the sons of Emmor [the father] of Sychem.