How can I create a URI for my iOS app, so that I can register it was the Instagram API under the field "redirect URI"?

This is something I've been working on for weeks now and I've decided to use my Treehouse to see if I can get some answers.

Here's what I'm trying to do: I have an iOS app, and I want the user to be able to login (authenticate) with their Instagram account using the Instagram API. There is a step in registering with Instagram that they ask for a "valid redirect URI."

Here's what I know: Some people have suggested doing a custom URL scheme, entering a value like: myapp:// ... but this doesn't work because Instagram API only accepts https:// values. So any of the "it doesn't matter, just put something in there" answers do not work. So then I think to myself, I have a website domain for my app, myapp.com, say, I can enter that as the "redirect URI," but I'm not sure if that is a valid approach.

If anyone can please help me understand this, it would be much appreciated. (Also, this particular problem seems to be bugging many people, because it's not adequately answered on StackOverflow).

Thank you.