The 21-year-old Panamanian international joined the Red Bulls on loan in February and had two goals in 17 appearances in 2017, playing both as a fullback and a center back. The option pickup had been expected.
"We are pleased to add Amir on a permanent basis," said Sporting Director Denis Hamlett in a statement. "He showed well and has made progress as a player during his time here. He is building on the positive qualities we saw when we were scouting him, and we look forward to him contributing to our success moving forward."