Financial technology (FinTech) has swiftly revolutionized mobile money as one of the ways of accessing financial services in developing countries. Numerous mobile money applications were developed to access mobile money services but are hindered by severe authentication security challenges, thus, forcing the researchers to design a secure multi-factor authentication (MFA) algorithm for mobile money applications. Three prototypes of native mobile money applications (G-MoMo applications) were developed to confirm that the algorithm provides high security and is feasible. This study, therefore, aimed to evaluate the usability of the G-MoMo applications using heuristic evaluation and usability testing to identify potential usability issues and provide recommendations for improvement. Heuristic evaluation and usability testing methods were used to evaluate the G-MoMo applications. The heuristic evaluation was carried out by five experts that used the 10 principles proposed by Jakob Nielsen with a five-point severity rating scale to identify the usability problems. While the usability testing was conducted with forty participants selected using a purposive sampling method to validate the usability of the G-MoMo applications by performing tasks and filling out the post-test questionnaire. Data collected were analyzed in RStudio software. Sixty-three usability issues were identified during heuristic evaluation, where 33 were minor and 30 were major. The most violated heuristic items were "help and documentation", and "user control and freedom", while the least violated heuristic items were "aesthetic and minimalist design" and "visibility of system status". The usability testing findings revealed that the G-MoMo applications' performance proved good in learnability, effectiveness, efficiency, memorability, and errors. It also provided user satisfaction, ease of use, aesthetics, usefulness, integration, and understandability. Therefore, it was highly recommended that the developers of G-MoMo applications fix the identified usability problems to make the applications more reliable and increase overall user satisfaction.