The initial public offering of payment-service company Nexi SpA raised 2.01 billion euros ($2.3 billion), making it the biggest listing in Europe so far this year and the third major IPO of a payment-processing institution in the region in less than a year. A mix of existing and new Nexi shares were sold to more than 340 investors from around the world, including more than 100 Italian investors. Nexi, whose investors include Advent International, Bain Capital and Clessidra SGR, will have free float of 35.6 percent.