NIAGARA FALLS — A 17-year-old city resident was robbed at gunpoint Saturday morning after trying to arrange a cellular telephone purchase. The victim, a Weston Avenue resident, told police he spent two days on the LetGo app arranging the purchase of an iPhone 8 plus for the price of $450. He was finally directed to an Ontario Avenue residence to make the purchase and went there with his sister just before 11 a.m. Saturday. Upon knocking on the door, the victim told police, a man wearing a dark hoodie over his head shoved open the door and dragged him inside before sticking a long gun into his midsection. The man demanded money, and took the $450 cash from the victim’s wallet before flipping the wallet back to him and telling him to run “or be shot.” The victim fled the scene and contacted police.