Nowadays security measures especially fraud detection has become an imperative issue in the design of online payment systems. In addition to standard network security schemes such as data encryption and firewalls, payment systems with internal logics that are capable of detecting fraud transaction, and even potential fraud transactions are preferred by both users and solution providers. Currently on the market one can easily purchase a software package for implementing an e-payment system with most standard payment functions. Fraud detection capability, usually implemented as an extra add-on internal logic in the system, however is not included in most packages. It would have to be built in-house. This paper sheds some light on the designing issues on this add-on fraud detection module, namely Fraud Detection Manager. The design is based on the concept of atomic transactions called Coupons that we implemented in e-wallet accounts. This is a relatively simple approach to deter fraud and resolve dispute without the use of digital signing [1]. Some issues in handling fraud transactions are discussed from our experiences in operating a commercial e-wallet service.