You showed him the Flower Book, but Von Leon is angry that you touched his belongings. It doesn't seem like he'll believe anything you say. According to Ifia, he was a nice, romantic person. What changed him like this?
Ifia found the Flower Book which she made with Von Leon in the rose garden a long time ago. She is certain that it will change Von Leon's mind. She says he will believe Ifia then. Go back to the Audience Room.