The changes are around cyber security apparently. Models with the newly required features have a -G at the end. This is from zappi:
2.2 What’s changed with zappi
The following features have been added to all zappis to comply with the Electric Vehicles (Smart Charge Points) Regulations 2021, Schedule 1, from 30th December 2022:
Set-up Wizard – The set-up wizard at power up has been changed to ensure smoother initial set-up. This includes internet connection and firmware updates upon start up.
Automatic Firmware Checking – zappi will regularly check for new software and will automatically display a message on your zappi screen to let you know in the myenergi app when updates are available.
Tamper Detection – We have added built-in tamper detection to alert you if anyone has removed the front cover of your zappi. You will be alerted in the myenergi app when tamper activity is detected.
Encryption – To protect your data from eavesdroppers zappi uses Advanced Encryption Standard (AES) to securely communicate throughout your home and across the internet.