FRANKFURT/LONDON, Jan 22 (Reuters) - Swedish payments firm Trustly is preparing to launch a stock market flotation in the second quarter in a deal potentially valuing the private equity-backed group at up to 9 billion euros ($11 billion), people close to the matter said. Buyout group Nordic Capital is working with Goldman Sachs , JP Morgan and Carnegie on the initial public offering (IPO) and is in the process of mandating more banks with a view of launching the deal in late April or early May, they said. Trustly may be valued at 6-8 billion euros, two of the people said, while another said it could fetch 7-9 billion. Nordic Capital and the banks declined to comment. (Editing by Mark Potter)