The extension fee is a fee to extend the single-use card transaction over a longer interest free period.
Purchases made using a Single-use card come with an interest free period of 3 months. However, you can choose to extend your instalments beyond the interest free period to 6,12 or 18 months for an extension fee, charged at a rate of 1% of the total purchase price per month.
If you later choose to opt out of Instalments within the guaranteed interest free period of 3 months, any extension fees previously paid will be refunded to your Zip account.