Introduction.

This case study details how I facilitated the successful unification of PayPay's fragmented business platform used by two million small merchants in Japan. Facing significant technical debt and inconsistent user experiences across web and app versions, I enabled cross-functional teams to transform the platform through collaborative leadership.

By creating space for technical innovation, establishing clear frameworks without micromanaging, and fostering distributed ownership, the project delivered a unified codebase with consistent user experience across platforms.

The project overcame significant technical challenges through team empowerment and adaptive problem-solving, ultimately creating a scalable foundation for PayPay's future merchant services growth while demonstrating the effectiveness of leading from behind.

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PayPay Digital Payment Platform: Market Context & Business Challenge.

PayPay has emerged as Japan's digital payment leader with approximately 50 million registered users and three million merchant partners. Launched just four years prior, its explosive growth quickly outpaced established competitors like Rakuten Pay and Line Pay through a keen focus on customer experience and substantial investment in cash back rewards.

Among its three million merchant partners, two million are small offline businesses operating just 1-2 stores each.When I joined PayPay in 2020 as Senior Product Manager, I inherited responsibility for the PayPay for Business (PPfB) platform. This system served as the primary interface for small merchants to manage their PayPay payment processing.

Initially, the platform only allowed merchants to view their sales history, reflecting the company's earlier focus on growing retail customer adoption rather than merchant services.

The platform faced a critical challenge. Before my arrival, PayPay had hastily developed and released a mobile app in response to merchant requests for additional services.

However, this created significant fragmentation as the app was built on an entirely different JavaScript framework than the web version. Adding to the complexity, the web version was maintained by an external vendor in India, while the app was developed by a newly formed internal team.

As I observed the day-to-day operations, I noticed this divergence wasn't merely a technical concern—it was creating tangible problems for our merchant community and development teams alike:

Merchants experienced inconsistent interfaces and capabilities
Development efforts were unnecessarily duplicated
Feature parity became increasingly difficult to maintain
Scalability for future services was severely limited. Services would be a key growth lever for PayPay

Rather than immediately asserting my solution, I began by creating opportunities for our technical experts to fully assess the situation's impact. Through collaborative discussions with various stakeholders, we collectively recognized that unification wasn't just addressing technical debt—it was establishing the necessary foundation for the platform's future viability.

Product Management Challenge: Identifying Platform Fragmentation Issues

The fragmentation created numerous challenges: Merchants experienced vastly different interfaces depending on which platform they used

Developers had to duplicate their efforts across both systems
Feature parity was impossible to maintain
The web version was built on AngularJS, which was approaching end-of-life

Rather than dictating a solution, I created space for our technical experts to assess the situation. By bringing together key stakeholders to evaluate the impact of these issues, we collectively recognized that unification wasn't just a technical debt concern—it was essential for the platform's future.

Cross-Functional Leadership: Building Stakeholder Alignment

Instead of pushing my vision in isolation, I focused on creating a shared understanding of the problems. This meant:

Facilitating cross-team dialogue: I organised discovery sessions where developers, designers, and business stakeholders could voice their concerns and identify dependencies.
Empowering technical leadership: I worked alongside the lead developer to conduct a comprehensive assessment, allowing technical experts to shape the approach.
Creating space for innovation: When overwhelmed by the project's scope, I asked open questions that enabled the team to find their own breakthrough solution—discovering that the app's hybrid nature could significantly simplify our approach.

Agile Project Management: Implementing the Platform Unification Strategy

Rather than micromanaging implementation, I established a framework that enabled teams to operate with autonomy:

Phased approach: We collaboratively developed a three-phase plan that grouped interdependent functions and allowed teams to validate their work incrementally.
Clear boundaries: I helped establish the core tenet of "porting and refactoring only," which allowed teams to focus their efforts and reduced unnecessary dependencies.
Distributed ownership: By clearly defining each team's responsibilities, members could take ownership of their contributions while understanding how they fit into the broader project.

Product Leadership Lessons: Overcoming Technical Challenges

When I overlooked engaging the Site Reliability Engineering (SRE) team early in the process, I approached this challenge with transparency. Rather than imposing a solution:

I acknowledged the oversight to all stakeholders
Invited the SRE team to share their expertise and recommendations
Created space for a passionate team member to step up with an API optimization solution
Collaborated on data analysis to develop a staggered rollout approach

FinTech Product Success: Measuring the Platform Unification Impact

The successful launch wasn't presented as my achievement, but as a team victory. I supported the deployment by joining the developers during the late-night launch—not to direct, but to offer moral support and acknowledge their critical role.

The unification project succeeded by bringing everyone's strengths to the table:

A single codebase with consistent UX across platforms
Stable launch without impacting our merchants, zero down time.
Foundation for future scalability of the PPfB platform

This collaborative approach to leading the unification project exemplified how creating the right conditions, asking the right questions, and empowering teams can drive significant organizational transformation—even when facing complex technical challenges.

PayPay Platform Unification