The authorization code is also the serial number. Here is how to query the serial number:
Tools/Materials
iPhone model iPhone8
iPhone system version ios11.4.1
1. Find the settings option on the phone. Open "Settings" and scroll down to see that there is a "General" that we choose to open.
2. Open "General" and find the first item on the panel, "About This Mac".
3. After opening, we can see the "serial number" by scrolling down. It’s that string of English plus numbers