Check imei not working

You can see your EMEI number by opening the Phone app, tapping the Numberpad, and typing *#06#. Your EMEI number is on the second line.

If you want to check your iPhone's serial number, you can find the serial number here:

Settings → General → About → look for Serial Number

You can enter your Serial Number here, and find information about warranty and coverage:

Check Your Service and Support Coverage - Apple Support