In recent decades, day-to-day lifestyle requires online payments as easy and simple solutions to several financial transactions, which makes the concept of Electronic payment Systems very popular in the growth of a cashless society. In fact, cashless transactions through simple mobile apps are not merely a concept anymore rather are implemented robustly and being used extensively. On the dark side, obvious financial benefits are making these apps vulnerable to being attacked, which can be successful through security breaches. These cybersecurity issues need to be traced out and resolved to make the financial transactions through an app secure and trustworthy. In this paper, several related papers are analyzed to trace out possible cybersecurity issues in the domain of Electronic Transaction System. The objective is to establish sufficient theoretical background to propose methodologies for measuring security issues and also identify the security strength of any FinTech application and provide standard security metrics.