The piece itself was sold to Italian art dealer Baldassare del Milanese, and then it was passed onto Cardinal Riario of San Giorgio. Controversy arose when it was determined that Michelangelo had artifically aged the sculpture using acid, which essentially was considered a form of fraud at the time and so the new owner was upset and demanded his money be returned.

Whether or not it was Michelangelo’s idea, the statue was artificially aged, and then sold as an antiquity to an Italian Cardinal, Raffaele Riario, who eventually realised that he had been duped. This, however, proved vital to the development of Michelangelo’s career. The Cardinal was mostly angry at Milanese, who was forced to give part of his money back. Michelangelo, on the other hand, was able to keep his share of the profits, and received an invitation to Rome from the Cardinal, which proved essential to Michelangelo’s career.

https://www.thehistoryofart.org/michelangelo/sleeping-cupid/