Where do I find the IMEI number?

International Mobile Equipment Identity (IMEI) Numbers
 
Purposes of IMEI are to identify mobile devices on a mobile network and to prevent theft. If a mobile device can be universally identified a thief cannot change the SIM card in a device and expect the stolen device's identity to go undetected. IMEI numbers are hard-coded into device hardware.
 
To find your device’s IMEI number follow these steps.

or at keypad dialer, key-in *#06#
 
Aside, the IMEI number can also be found on the back of the device or behind the battery.
 
Without IMEI, the device will not be able to connect to network connectivity. Call and data is not accessible.
 
If your phone encountering "Invalid IMEI", we recommend to perform factory reset.
 
After factory reset and "Invalid IMEI" still appear, please send your phone to your nearest service center location.