In a study from Pymnts.com, 5.5% of iPhone users said that they had used Apple Pay at participating retailers in June, up from 4% in March and 4.5% in October 2016. Walmart Pay, the retail giant’s mobile payment alternative, attracted 5.1% of Walmart shoppers in June. That was up from 3.3% in March. In an interview with Bloomberg, which earlier reported on the study, Walmart senior vice president of services and digital acceleration Daniel Eckert said Walmart Pay should soon pass Apple Pay for usage at participating retailers, making the retail giant’s service the most popular in the U.S.

Eckert’s comments were echoed by Richard Crone, a researcher who monitors the mobile-payment market, who told Bloomberg that Walmart Pay should be bigger than Apple Pay by the end of next year.

Like Apple Pay, Walmart Pay is a service that allows users to make purchases from their smartphones without ever taking out a credit card. However, Walmart Pay is exclusive to Walmart stores. Apple Pay is available at a variety of retail stores, including the Apple Store, Walgreens, Best Buy, and others.

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When Apple Pay launched in 2014, the iPhone maker pitched the service as a secure and desirable alternative to credit cards. And soon enough, Apple was lining up retailers to support the service with the idea that there are hundreds of millions of iPhones in use and many of them could be used to make payments. Some retailers were anxious to adopt Apple Pay and the service’s usage has been growing.

Walmart, however, wasn’t so quick to jump onboard and has never offered Apple Pay support. While Walmart hasn’t publicly commented on why it’s turned its back on Apple Pay, its decision in 2015 to launch Walmart Pay suggested the retailer was ready to do battle.

Apple hasn’t publicly discussed Walmart’s decision, but the world’s largest retailer’s conspicuous absence has been hanging over the mobile payments service since its inception. According to Bloomberg, citing a source, Apple and Walmart held discussions through March 2016 to bring Apple Pay to the retailer’s nearly 5,000 stores, but talks ultimately broke down.

While it’s possible that Apple and Walmart might eventually come to terms, for now, the companies seem content to compete. And judging by the latest data, Apple might be fighting a losing battle.