By Karuna Murti & Rory @ Cash I/O Team & Payment Team Merpay Backend Introduction

Self-Introduction My name is Karuna Murti I’m from Indonesia Working in tech since 2005 Worked with people from dozens of countries and dozens of cultures Hobby is hiking and Star Trek

Self-Introduction Hi, I’m Rory! 👋 Originally from the UK, in Tokyo since April. Studied Computer Science at universities in the UK and Finland Working history primarily in tech consulting as a SWE Passionate about skiing, formula 1 and running

　　 Businesses
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　　 Merpay　 5

Mission

What is Merpay? Merpay is a mobile payment service brought to you by the creators of Mercari, Japan's largest C2C marketplace app. It is operated by Merpay, Inc., under the Mercari Group. With Merpay, users can make payments on Mercari and at 2.64 million stores nationwide, by using the money earned from selling items they no longer need on Mercari, charging money from their bank accounts, or using Merpay Smart Payments. 7

Mercari Group’s “Circular Finance” 画像の英訳： 好きなこと・やりたいこと＝ User’s dreams 出品 = List モノ = Items お金 = Money 決済 = Payment 信用 = Credit 利用実績 = Usage history 信用情報 = Credit information 売上金= Sales balance The addition of Merpay to Mercari’s item lifecycle creates a circular relationship between users’ items, money, and credit, facilitating the growth of “circular finance” that grants users greater freedom and flexibility. It provides users with a valuable, uniquely Mercari experience. 
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Merpay’s Three Focus Areas ● Lump-sum payment: 　Defers payment to the following month ● Fixed-amount payment: 　Pay in installments over several months ● Started services allowing users to 　use their Merpay balance for 　asset management and more Payment Credit Growing Wallet Lump-Sum Payment Fixed-Amount Payment Asset Management Pay for everyday purchases all at once the following month Treat yourself now and pay over several months at a fixed amount of your choice ●Providing a virtual card in addition to iD payment and code payment iD Code Payment Hold your phone over a reader Scan a code Virtual Card Input a number 1. Launched March 3, 2021 9

Payment

Merpay's Users The number of Merpay users1 is 12.92 million, with an 80% retention rate for first-time users2. 1. Total number of unique users who are registered for Merpay Electronic Money, or used Merpay Code Payments, Online Payments, Merpay Smart Payments, etc. as of Sep 2021. 2. The ratio of unique users who made a payment using Merpay for the first time at an offline merchant in May 2019, and made a payment using Merpay again the following month. This does not include users who made their first payment entirely using points awarded for free. Retention Rate of First-time Users Number of Users Over 12 million Merpay users 11

*Includes select store locations where Merpay is not available. Merpay's Merchants 2.64 million locations nationwide (March 2022) and more... 12

Primary ↔ Secondary Distribution Cycle Receive money for sale/charge balance Receive item Sell unneeded items on Mercari Purchase new items using Mercari sales balance, etc. 13

How to pay for something in Merpay ● Merpay balance ● Bank transfer ● Credit Card ● Apple pay ● Deferred payments ● Monthly installments ● Points from third party systems And others…. But all of these need to work consistently, reliably and provide a good experience for our users. We also need need to ensure our systems are secure, and easily auditable. 14

Payment Core is the “beating heart” of these transactions For all items bought on the Mercari app or sites… For all payments made using Merpay to buy items… We will make sure that money goes from place A to place B quickly and securely. That’s A LOT of payments to handle! 15

What kind of things do we deal with? Scalability - our features need to be able to operate efficiently for our millions of users. Even small changes can have a large impact on the UX of Merpay! Transactional consistency - how can we ensure that when something goes wrong, all of our backend microservices have been correctly updated? 16

So, what have I enjoyed the most? ● Helping Japan move towards a cashless society ● Working on products with scale ● Always new challenges, new features and room to grow ● Great colleagues! 17

What Cash I/O team do Cash I/O responsibility is connecting Mercari Group ( Mercari, Merpay, Mercoin, Souzoh, etc ) with financial institutions (Banks, ATMs) and managing the connections afterwards. 18

What Cash I/O team do Cash I/O major functions Cash In - Funds Recharge - Topup Cash Out - User Payout - Partner Payout 19

Cash In Functions - Bank Account Registrations - Funds Recharge - Providing data to other services - Connecting hundreds of banks (300+) - Handling … funds recharge requests / s - Ensuring the availability and reliability of the services - Ensuring people’s money is in the right place

Cash In 21

Cash Out Processors User Payout Partner Payout 22

Credit

Merpay Smart Payments - A Credit Service Based on “Trust” *Deferred payment is not available to users under the age of 18. Users 18 or 19 years of age also have an upper usage limit of 50,000 yen and require the consent of their parent or guardian. Fixed-amount payment is not available to users under the age of 20. Total usage limit for deferred + fixed-amount payments is 300,000 yen. 24

Merpay Smart Money - Small-sum Loan Based on Mercari Usage *Maximum borrowing limit is 200,000 yen. Interest rate and borrowing limit are determined through a screening process based on the user’s Mercari usage history. Not available to users less than 20 years of age or over 70 years of age. 25

Growing Wallet

Merpay Engineering Organization

Organizational Structure Cash-out Merchant Platform Product classification Backend 1 Backend 2 iOS Android Functional classification PM PM PM TL TL EM EM EM EM TL 28

Architecture Tech Stack ● Microservices ● Google Cloud Platform ● Kubernetes (GKE) ● Cloud Spanner ● Go ● gRPC 29

We Are Hiring!

New Tech Big Scale Grow Together The Charm of Merpay 31

Who share the mission of “Building trust for a seamless society” and want to commit to it together with us. Who are willing to understand the complicated and difficult FinTech domains and has the passion and confidence to solve the social problems with technology. People we want 32

Thanks!