Mercari cuts iOS CPA in half with AppsFlyer and Meta AEM

Overview

• Mercari’s cross-border team launched its first global app in September 2025, appealing to overseas fans of Japanese anime, comics, and games. 
• iOS 14.5 and ATT left the team measuring only 20-30% of iOS installs without modeling, making it difficult to prove Meta’s iOS performance to non-marketing stakeholders and, at times, shifting budget away from iOS. 
• Ahead of US and EU launches, Mercari implemented Meta’s Aggregated Event Measurement (AEM) via AppsFlyer to restore conversion visibility and establish a consistent measurement standard across all markets and channels. 
• As a result, iOS cost per acquisition (CPA) fell by roughly 50% while buyer volume held steady, freeing the team to scale iOS spend beyond Android in various markets and prove budget decisions with validated data. 

Background

Mercari is Japan’s leading consumer-to-consumer marketplace. In September 2025, it launched its first global product: Mercari Japan, a cross-border app that lets shoppers abroad buy directly from sellers in Japan. The app launched in Taiwan and Hong Kong, then in the United States. Mercari plans to expand to 50 countries within two years.

Mercari’s audience is primarily made up of fans of Japanese anime, comics, and games, drawn to their large inventory and quality pre-owned goods. To reach their audience, Mercari’s cross-border team built its acquisition strategy around prioritizing new buyers, not just installs. iOS usage is high across Mercari’s launch markets, so the team prioritizes iOS delivery, with Meta as one of its most important channels.

Challenge

In 2025, Mercari was operating in a post-ATT world, where iOS 14.5 had fundamentally changed mobile measurement. By the team’s estimate, 40-50% of iOS conversions were not being recorded, and without any modeling in place, the team could only measure an estimated 20-30% of iOS installs. In addition, limited SKAdNetwork data made it difficult to break down performance by market or in-app action across the initial launch countries. The Mercari team anticipated that the issue would only grow as they pursued their goal of expanding into 50 countries.

The measurement gap didn’t just make reporting harder; it also affected budget decisions. The marketing team could explain the shortfall internally using benchmark values and past conversion rates. However, explaining that to corporate planning, product, and executive teams was a tougher sell. Without solid proof of what was really happening on iOS, budgets sometimes shifted to Android and web, even when iOS was likely performing just as well or better.

Solution

With US and EU launches planned for the same year, Mercari knew the measurement gap would be even bigger in those markets than in Taiwan and Hong Kong. To proactively mitigate potential measurement issues, the team implemented Meta’s Aggregated Event Measurement (AEM) via AppsFlyer, providing a solid foundation that enabled them to measure more iOS conversions before expanding further into new markets.

Aggregated Event Measurement is a Meta protocol for measuring web and app events from people on iOS 14.5 and later devices. It lets AppsFlyer attribute iOS install events to Meta ads for devices that have opted out of ATT, covering both single and dual opt-out devices, using last-touch attribution with a 24-hour attribution window. No user-level identifiers are involved.

AppsFlyer unifies Meta’s AEM signals with its own modeling in its Single Source of Truth layer, alongside SKAdNetwork and other sources. For Mercari, that meant visibility into iOS conversions that ATT had otherwise obscured, without depending on opt-in rates.

The implementation process was smooth, with setup taking less than a month. Mercari’s team switched from another measurement provider and found AppsFlyer’s dashboards and documentation much easier to use, while dedicated support meant there were no technical delays.

The bigger value was consistency. “Individual media platforms all operate on their own attribution logic,” says Shuhei Ezoe, Marketing Manager, Mercari. “Using AppsFlyer as an independent, third-party standard lets us evaluate performance the same way across every channel. That consistency becomes even more important as we scale from Taiwan and Hong Kong to the US, the EU, and eventually 50 markets.”

Results

Cutting iOS CPA in half

Comparing performance before and after implementing Meta AEM via AppsFlyer, Mercari cut its cost per acquisition (CPA) on iOS by roughly 50%. The biggest gains came from Meta iOS campaigns, with new buyer volume remaining steady even as costs dropped.

Recovering lost iOS attribution

Once Meta AEM went live through AppsFlyer, Mercari’s attributed iOS installs increased by 167%. That means AEM-attributed installs now account for roughly 62% of Mercari’s measured iOS installs, giving Mercari a clearer picture of what was actually happening on iOS all along.

Scaling spend without cannibalizing Android

Improved measurement through Meta AEM gave the team the confidence to invest more in iOS. Because efficiency improved, that extra investment didn’t come out of Android’s budget. Rather, total marketing spend grew. In some markets, iOS budget now exceeds Android’s, a reversal from before Mercari introduced AEM. The team also combined several market-specific campaigns into broader ones.

“The investment allocated to iOS now exceeds that of Android across select target markets. Android historically commanded a larger budget share due to data visibility, but that dynamic has now inverted.” 

– Shuhei Ezoe, Marketing Manager, Mercari

Removing an internal roadblock

One of the biggest shifts was organizational, as the team can now show executives real, validated ROAS numbers, so budget conversations that used to stall move forward much faster.

“Because we can now show legitimate, validated ROAS metrics across our channels, Meta included, and demonstrate that to leadership, the barriers that used to slow us down have been removed.”

– Shuhei Ezoe, Marketing Manager, Mercari

Mercari’s results reflect what the two solutions accomplished when working seamlessly together. Meta AEM gave the company’s ad delivery a fuller, privacy-safe view of iOS conversions, while AppsFlyer gave the team a single, independent standard to measure and trust those results across every channel. Together, both solutions turned a gut feeling of “we think iOS is working” into trusted data the whole company could act on.

What’s next

With more of the iOS funnel now visible and measurable, Mercari is retesting dynamic product ads, investing more in feed-based formats, and evaluating other privacy-focused measurement tools, including Meta’s Conversions API. The goal is to strengthen measurement further ahead of its EU launch, where ATT rules are strictest.

“If Meta is already making a meaningful commercial contribution to your business before enabling AEM, implementing it will almost certainly show an even higher, more accurate level of that contribution on iOS. That extra visibility is only useful if you can act on it. For us, that meant pairing Meta AEM with an independent measurement layer like AppsFlyer. There’s no real reason to hold off.” 

– Shuhei Ezoe, Marketing Manager, Mercari