Buying a JUDLEX licence means choosing three things: the level, the seats — one for each computer that will open the application — and whether you pay monthly or yearly. The price now comes from the offer JUDLEX has published at that moment, with the seats it includes and its terms for paying yearly, and the screen shows you the subtotal, the tax and the total before it asks for your card. On Linux you finish the payment in the system browser; on macOS and Windows the card form stays inside the application.
On Linux the payment finishes in the browser
On Linux, when you choose “Buy”, JUDLEX opens the payment page in the system browser. On macOS and Windows you pay inside the application, and JUDLEX only turns to the browser if that form does not load.
The offer sets the price
The offer is what JUDLEX has published at any given time: which licence levels there are and what they cost. The application sends the server the level, the seats and the period you choose, and the server works out the amount; the application does not decide the figure.
The total is itemised before you pay
Before it asks for your card, the payment page shows you the amount before tax, whatever tax applies and the final total, in the currency you will be charged in.