Facebook will end a controversial market research program that violated Apple developer guidelines in order to harvest user data from the phones of volunteers. The company said early Wednesday evening that the Facebook Research app, which offers volunteers between the ages of 13 and 35 monthly $20 gift cards in exchange for near-total access to the data on their phones, would no longer be available on iOS. It will apparently continue to be available for Android users.

TechCrunch reported on Tuesday that the company has been paying the gift cards to people aged 13 to 35 in exchange for installing an app called Facebook Research on iOS and Android. The app monitors their phone and web activity and sends it back to Facebook for market research purposes.

Facebook previously collected similar data using Onavo Protect, a VPN service that it acquired in 2013. The company has used the data to identify up-and-coming competitors, then acquire or clone them. Facebook removed the app from the App Store last summer after Apple complained that it violated the App Store’s guidelines on data collection.

The Research app requires that users install a custom root certificate, giving Facebook the ability to see users’ private messages, emails, web searches, and browsing activity. That’s in apparent violation of Apple’s system-level functionality, which is intended to grant employers access to employees’ work devices. The policy prohibits developers from installing the certificates on customers’ phones.

In a statement, Facebook objected to parts of TechCrunch’s report.

“Key facts about this market research program are being ignored,” the company said. “Despite early reports, there was nothing ‘secret’ about this; it was literally called the Facebook Research App. It wasn’t ‘spying’ as all of the people who signed up to participate went through a clear on-boarding process asking for their permission and were paid to participate. Finally, less than 5 percent of the people who chose to participate in this market research program were teens. All of them with signed parental consent forms.”

The company also denied that Facebook Research was intended to replace Onavo, although it did not respond to evidence that the apps shared similar code.