You're summoning on the wrong focus page. When you go to the summoning page you need to select a page that inhibits the likeness of receiving a higher class hero for the focus. There is two different pages. One for Robin, Marth, Lucina, and Tiki. You have to click the aero to switch the summoning page so you can have the right focus page to get Lyn. Once you're on the page with the illustration with Camillia, Takumi, Roy and Lyn. Then you summon. I hope this helps.