Greetings, Lucchi.
It appears you haven't received the verification code to authorize wwo-factor authentication to use your Apple ID on your iPhone 4s. I'll be happy to help you with this.
Two-factor authentication for Apple ID
How it works
With two-factor authentication, your account can only be accessed on devices you trust, like your iPhone, iPad, or Mac. When you want to sign in to a new device for the first time, you'll need to provide two pieces of information—your password and the six-digit verification code that's automatically displayed on your trusted devices.
A trusted device is an iPhone, iPad, iPod touch with iOS 9 and later, or Mac with OS X El Capitan and later that you've already signed in to using two-factor authentication. It’s a device we know is yours and that can be used to verify your identity by displaying a verification code from Apple when you sign in on a different device or browser.
Get a verification code and sign in with two-factor authentication -- There are two ways you can have a verification code sent. Follow the steps under "Get a text or phone call" or "Get a code from Settings on your trusted device".
Have an excellent day!