BusinessEl Salvador’s roll-out of bitcoin as legal tender got off to a shaky start.The Central American country is the first in the world to adopt the cryptocurrency as an official means of exchange; it now uses bitcoin alongside the American dollar.Systems were overwhelmed as people downloaded the government-backed Chivo, or “cool”, e-wallet, after the government offered $30-worth of free bitcoin as an incentive.The roll-out added to already volatile trading in bitcoin; at one point the price plunged so fast it was described as a “flash crash”.Coinbase, a cryptocurrency exchange, revealed that America’s Securities and Exchange Commission is threatening to sue it, if it brings a product to market that allows users to lend their cryptoassets and earn interest on the loan.The company suggested that this may be because the SEC classifies the product as a security (therefore falling outside existing lending regulations), but it had not been given an official explanation.SoftBank’s stock surged after it announced a complex deal that gives it a 4.5% stake in Deutsche Telekom in return for a chunk of its shares in T-Mobile US, in which Deutsche Telekom is already the largest investor.