Welcome to the Forum, @kaylabaustin12! 
I see that it’s been a few days since you posted. Have you found a solution?
I don’t use iOS, and it seems like you’ve done some appropriate troubleshooting already, but my guess from the error message in your screenshot (very helpful, so thanks for including that!) is that the login process is failing at the point where the browser (where authentication takes place) is trying to pass a token back to the app (at least as I understand it), so that strikes me as a browser settings issue.
Two topics that come to mind are one where some pop-up blocking and cookies settings were changed in Safari and another where Android login issues were attributed to a default browser setting for allowing links to open in external apps. With that in mind, I’d go poking around in Safari’s settings and try things like this:
- Check/change pop-up settings.
- Check/change cookie settings.
- Look for a setting that allows links to open in external apps and enable that.
- If none of that pans out, then I’d look for a way to reset or “refresh” Safari back to its default settings.
- If that still doesn’t work, then I’d try setting a different Web browser as the default browser.
That’s the approach I think I’d take, anyway. In the meantime, I’m also going to tag in @Antonius and @habib, because they’re the first two iOS users who immediately come to mind.