I've got no need to sign up to get more spam.
I'm also not sure if an iOS app is the way to do it. Why should I download an app that joins the cluttered mess of twisty little icons that all look alike on my iPad (making it harder to find the apps that I really do use regularly) for some need I only have sporadically.
What advantage does this have, for either the customer or the vendor? What if either of them uses Android? Would it be better to do this on a big wide monitor on a computer or to do it on some tiny screen?