You will need to add a credit card to your account prior to configuring automatic pre-paid top-up's. Please see the following knowledge base article for instructions on how to do so...
To configure automatic pre-paid account balance top-up's log in to Portal - http://portal.neural.net.au and follow these steps...
1. Select the "My Account" tab
2. Select the "Top Up" menu option
3. Specify your automatic top-up settings
4. Click "Save Settings"
It may take up to 15 minutes for your automatic top-up to be processed. In the interim you may opt to process a manual top-up using the options to the left.