Apple sets App Store prices in fixed steps, so the app charges the step nearest our website price, which is not always exactly the same.
On licento.com you pay the price shown on the exam's page, VAT included. In the app, the App Store charges its own price: we place each exam at the App Store price nearest our website price, and Apple shows it in your own currency.
So the two can differ a little. The buy button in the app always shows the price Apple will charge.
What you get is the same either way: the exam for good, open on every device signed in to your account, with the same period of Premium.