The operator of Seven-Eleven convenience stores in Japan said Thursday possibly some 900 customers using its mobile payment service have lost a total of 55 million yen ($510,000) due to unauthorized access to their accounts.The problem surfaced soon after the operator, Seven & i Holdings Co., launched the smartphone payment service "7pay" at over 20,000 stores across the country on Monday, potentially forcing it to review its digital marketing strategy including its cashless payment service.Police arrested two Chinese men on Thursday in connection with the problem, investigative sources sai…READ FULL ARTICLE