A lawyer for R. Kelly struggled on Monday to convince a U.S. appeals court to overturn the former R&B superstar’s sex trafficking conviction and 30-year prison sentence.

Kelly, 57, is appealing his September 2021 conviction by a Brooklyn, New York, jury on all nine charges he faced, including racketeering and eight counts of violating the Mann Act, which forbids transporting people across state lines for prostitution.

His lawyer Jennifer Bonjean told the 2nd U.S. Circuit Court of Appeals that federal prosecutors failed to prove that the singer led a racketeering scheme where he recruited underage girls for sex and then violated several victims.