According to the OSB, the Synoptic Gospels say Christ's crucifixion happened on Passover, and during Preparation on the Gospel of John.
Why is there a contradiction?
Looking at it logically, the Jews would never have done anything let alone Crucify Jesus on the Passover.
Therefore it would have to be understood, it was the day before the Passover which would take place at sunset, this then makes it the Day of the Preparation.
Mat_27:62 Now the next day, that followed the day of the preparation, the chief priests and Pharisees came together unto Pilate,
Mar_15:42 And now when the even was come, because it was the preparation, that is, the day before the sabbath,
Luk_23:54 And that day was the preparation, and the sabbath drew on.
Joh_19:14 And it was the preparation of the Passover, and about the sixth hour: and he saith unto the Jews, Behold your King!
Therefore, when it is said Jesus was Crucified on the Passover, He was, to Western World thinking because, we do not separate the days by night and day but by time. (12:00AM - - 12:00PM