MILAN (Reuters) -Italian bank BPER Banca said it had received a non-binding offer for its merchant payment business from fast-growing payments giant NEXI, which one source earlier said could be worth around 350 million euros ($397 million). BPER, Italy’s fifth-largest bank, said it had given NEXI two months exclusively to submit a binding offer. Italy’s NEXI already runs BPER’s shop payments services through a commercial partnership. The deal is part of NEXI’s strategy of buying the payment assets of its banking partners, while keeping contracts in place with the lenders so as to pocket the op…