There are a few different ways how you can top up your Travel Union account.
You can add your credit or debit card information - just like a simple payment, you will be able to add a selected sum whenever it is necessary.
Your account can be topped up by a transfer to your account - you simply need to provide your name and the IBAN, which is located in your Settings page or visible after pressing the "Add money" button.
You can send a request to your fellow Travel Union users by using the option in "Add Money". The transactions should be reflected in your balance immediately.