My banking app on my telephone only is showing a box with the following (“WARNING” Sorry, but you must upgrade to the latest version of the app of before continuing. You can visit iTunes App Store to download the latest version of this app” scam?

Perhaps avoid confusion by contacting your Bank directly.

Their customer service may/not be helpful; but should be.

The bank may have afforded a newer better secure App.

An online prompt may be phishing for your information.

[You should verify which version iOS your iPhone runs.]

Maybe yours is older phone; is a newer iOS available?

This would generate a real notification & no phishing.

Outdated phones won't have newer App store updates.

If it just takes you to the App Store to download an update then there is no problem. This message is fairly common and routine. If you find yourself on some website (even if it looks legit) then it's probably a scam and you should not engage with it.