IMEI is an abbreviation for International Mobile Equipment Identity. It's a unique number that all mobile phones have. It's not the same as the serial number, but with IMEI we can retrieve additional information, such as the current value of your phone. It's therefore important that you carefully check that it's the correct IMEI number you are entering. It's 15 digits long and you'll find it in your phone's settings.
How to find the IMEI number..
Open the Settings app, select General and then About. Scroll down a bit to see the IMEI.
Open the Settings app, scroll down and select About phone. Scroll down further to find the IMEI number.
Start on the Home screen and swipe from right to left to open the Start menu. Scroll down and select Settings. Under System, click About and select More information to see your IMEI number.