The €45 requested when choosing to pay the toll post-paid by credit card is not a payment, but a pre-authorisation: this means that Satellic asks you to reserve an amount of €45 on your credit card.

This amount will start to decrease when you begin to drive on the Belgian roads since it is being used to pay for the kilometres driven.
When the remaining reserved amount reaches €7 (the warning limit), another pre-authorisation of €45 will be triggered. These pre-authorisations are a guarantee that the available limit on the credit card will be sufficient to pay the toll upon billing (twice per month).