Although he had already earned his first senior cap, Trapp was called up by the U23 national team for the first time in March 2015. He was a part of the team that placed third at the 2015 CONCACAF Men's Olympic Qualifying Championship, and was then called up to take part in the 2016 CONCACAF–CONMEBOL play-off against Colombia. Trapp wore the captain's armband for both games, culminating in a 3–2 aggregate defeat for the Americans that sent Colombia to the Olympics. He earned seven caps while eligible at U23 level.