You’re doing it right, you must use a external program to read QR code, and go to the link provided to check the Ticket.
Your user (the one you loged in your phone must have grant permisions to verify tickets, you can do it via your admin panel in wordpress:
Users -> (Select user to grant permisions)
(near the end of the page) Grant My Tickets Permissions
“Tick” Can verify tickets
Hope it works.