A 17-year-old was slashed inside an East Harlem subway station on Friday during a sneaker deal gone bad, authorities said.

The teen thought he was going to sell his kicks to a group of guys he met on social media — but the customers tried to rob him, law enforcement sources said.

The teen put up a fight until one of the customers pulled a knife inside the 125th Street station at 5:26 p.m., authorities said.

The victim was slashed in the shoulder and his attackers fled into the streets above, authorities said.

He was taken to New York–Presbyterian Hospital and was expected to recover.