The CST is available online. To download one, go to the CovidSafeBe app, masante.be or the Réseau Santé Wallon (Walloon health network) website.
You can show your CST using your smartphone or by printing it out at home before you come.
You can also request a paper version by post by calling 071 31 34 93.
More information (in French) https://www.wallonie.be/fr/actualites/application-du-covid-safe-ticket-dans-divers-secteurs-en-wallonie