When you sign in to some websites and apps, a one-time SMS passcode is sent to your iPhone. As a security measure, you’re required to enter the code into the website or app.
You don’t have to switch to Messages to copy it, though. iPhone can detect the passcode in Messages and display it above the keyboard, ready to use.
Note: Thanks to Continuity, SMS and MMS messages you send and receive on iPhone can show up on your Mac and your other iPhone, iPad, and iPod touch devices, too.
