Beautiful Jaime,
very thanks for your help! But, excuse me, my website is in a different language than English (Czech). Text “Scan this QR code at the event to check in” in the plugins file /wp-content/plugins/event-tickets-plus/src/Tribe/QR.php is in English, but in the ticket-mail is in Czech language (“Registrace na akci – Při vstupu na akci naskenujte tento QR kód pro registraci”), and I don´t know where the Czech text can be overwritten… Probably in the themes, but I can´t find where 🙁 I apologize for the problems and your time…