The recently added feature to the app that allows a player to launch an attack with a spell already cast is a little buggy for the app. The app will not allow you to use any spell you want, only spells from the god in that city. This is an example image. The city god is Athena, so when I selected heroic power there was no error message, but in trying to select another spell from a different god, it will not let me launch the attack and displays the error message in red text. EDIT: When I took the screenshot I had enough Hades favor to cast the Helmet of Invisibility, so lack of favor was not the issue.