I am creating an event booking site on WordPress:
User clicks on a Book Now on a event page on WP website.
He lands on external page where he can see:
Title of event(prefilled and uneditable),
Event id (hidden) (prefilled),
Currency preselected by default
Once he clicks on Pay on this page, It will fetch the price of the event from DB and then multiply with 5 and the make a call to an external page.
Read more here:: Passing data from a page to an external link