I have tickets for this Sunday's XFL game at MetLife for the Guardians and just download the Ticketmaster app. You'll find your tickets under My Events and then click on them and click on show barcode where a blue line moves back and forth over your barcode and it specifically states on the ticket "screenshots will not get you in."
The Red Bull app will also have the tickets as well as Ticketmaster is imbeded into the app itself. I have the XFL and NHL app does the same thing as well. I wish their was a unified MLS app which allowed you to choose the team you support and manage your tickets through that with the ability to switch teams if you happen to go to a road game. Its annoying to download the app of every specific team in the league. The NHL app works with most teams in the NHL for ticketing. The exceptions are the teams that dont use ticketmaster like Vegas, Philadelphia, and Montreal