Tickets to Rock Werchter 2021 are exclusively available from www.ticketmaster.be. A combi festival ticket (valid from 1 to 4 July) costs 243 euro (service charges and mobility fee included).
Each e-festival ticket allows you to download one free e-train ticket for public transport (train/festival bus) in Belgium. More info on that can be found here.
Important: if you wish to stay on one of the festival's campsites, you'll need to purchase a camping ticket as well.