My iOS its not supported what do I need to do?

What version of iPhone do you currently have? What version of iOS do you currently have?

If you go to Settings>General>Software Update and it shows that you are up to date, then your iPhone is probably not compatible with the latest iOS, which at this time is iOS 15.3.1. My guess is that you have an iPhone 6 or below, which cannot be updated any higher than the iOS you currently have.

If you need a higher iOS to do something with an app or a particular website, you will have to purchase a new iPhone.

Exactly what were you doing when you saw this message? What was the precise wording of the message?

What model iPhone? What current iOS version?