Make sure you enable the auto top-up checkbox after successfully paying with your credit or debit card. We will automatically charge your account $8 when your Yolla balance drops below $1. If you enable the auto top-up function through the website, the default amount is $8. You can change this later in the app.
You can disable auto top-up at any time on the Yolla website in the My balance section. Android app users can also switch it off in the Payment settings section of the Yolla app side menu.