You don’t need to put anything in it. Just register for an account, add a card and it’ll get automatically debited when you cross. I did this after I forgot and got finedJust been on the phone to them trying to sort out their mess of a website. We crossed yesterday and are in Norwich now. It’s a frustrating experience. I think I’ll open an account and stick a few quid in there to save all this hassle every time I cross (not often but I’ll be back for the Ipswich game).