Then came the Day of Unleavened Bread when the Passover must be killed. (Luke 22:7)
The day of the Unleavened Bread festival when the Passover is killed is the Preparation Day.
The Passover is killed the afternoon of the 14th, dressed out, taken home, roasted and eaten that night after sundown.
Jesus and his disciples did not keep the Passover they kept this Passover. Scripture does not say what they ate but after supper Jesus instituted this Passover, the one for the church.
Paul said, "For indeed Christ, our Passover, was sacrificed for us. Therefore let us keep the feast, not with old leaven nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth."
The church is prohibited from keeping Israel's Passover so Jesus instituted a new covenant Passover for the church. Jesus had to keep his Passover a night early because he was to be the Passover to be sacrificed the next day when the Mosaic Passovers were sacrificed.
Totally absurd!