To top up your meter, you first need to add credit to your electricity key or gas card. You can do this anywhere you see a Paypoint or Payzone sign. You can find your local Paypoint through your postcode. You can also find your closest Payzone the same way.
If this is your first time using your Bulb key or card, we have an article on the steps to follow.
Once credit has been added to your key or card, pop it into your prepayment meter. Make sure the gold chip on your gas card is facing up. Then press A to complete the top up.