Yes. GUTS' tickets are protected against illegal resale and price change from external parties. To register that you are the owner, an active internet connection is required.
GUTS ensures that there is always a working WiFi connection available at the events.
You can share your tickets on forehand. So if you don't have internet on your phone but your friend who is joining you has, share the tickets and make sure you can get in!
Do you not have a smartphone? No problem. Bring the phone you used to buy the tickets to the theater, and sign up at the (cash)desk.