imei.cs

        private string GetImei()
        {
            var permissionCheck = ContextCompat.CheckSelfPermission(this, Manifest.Permission.ReadPhoneState);
            if (permissionCheck == Permission.Denied)
            {
                ActivityCompat.RequestPermissions(this, new[] { Manifest.Permission.ReadPhoneState }, 0);
            }

            var mTelephonyMgr = (TelephonyManager)GetSystemService(TelephonyService);
            if (Build.VERSION.SdkInt >= BuildVersionCodes.O)
                return mTelephonyMgr.GetImei(0); // Some phones has more than 1 SIM card or may not have a SIM card inserted at all

#pragma warning disable CS0618 // Type or member is obsolete
            return mTelephonyMgr.DeviceId;
#pragma warning restore CS0618 // Type or member is obsolete
        }