Good news! Your Landis + Gyr EM5100 meter is compatible with the Powerpal
The pulse rate to enter into the app is 1000 and you can use the rectangular mount to attach your Powerpal to your meter.
Simply attach the mounting plate over the LED 1 Wh/imp (marked) on your main consumption meter so you can line up the output through the hole in the bracket. Then gently twist your Powerpal's sensor clockwise into place.
See the image below.
Then head to https://www.powerpal.net/install and follow the instructions to complete your installation.