By Luc Olinga,Martin Baccardax The federal agency opposes crypto industry demands to offer investors direct exposure to real underlying Bitcoin reserves. The U.S. Securities and Exchange Commission rejected a proposal from Grayscale to list a spot Bitcoin ETF on the NYSE Arca exchange, setting up a potential legal battle with the country’s biggest digital asset manager. The SEC said Grayscale’s request for an ETF listing, which it proposed as a conversion of its popular Grayscale Bitcoin Trust GBTC, didn’t meet the regulator’s standard of being “designed to prevent fraudulent and manipulative …