The retail giant said over the weekend that it plans to stop supporting its Underground Actually Free program, which debuted in 2015. At the time, Amazon pitched the program as a way for app developers to make money while giving away their software for free via Amazon’s online app store.

Under the program, participating developers could make their apps available through Amazon’s app store, and Amazon (AMZN) would pay those developers royalties based on the number of minutes people used their free apps.

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In order to have qualified, developers needed to already have a non-free mobile app available on either Google’s (GOOG) Play store or Apple’s (AAPL) app store, and ensured that their apps would work on “at least one non-Amazon mobile device”—and not just Amazon devices like Fire tablets.

The idea was to reward developers for building compelling apps while convincing consumers to download their apps from Amazon’s app store instead of through rivals like Google or Apple. Amazon’s hope was that consumers would be lured to its app store because some apps there would be free.

Some of the apps available from the program included popular mobile video games like Goat Simulator, Sonic Dash, and Castle of Illusion Starring Mickey Mouse. These apps normally cost money to download via competing app stores.

Amazon did not say why it was discontinuing the program, but it seems that it didn’t catch on with enough consumers.

Additionally, Amazon is debuting similar programs in which it pays developers to build apps, or skills, that improve the company’s Alexa digital assistant that people can speak with to do things like play music or order food. The retail giant could be shifting its resources to attract more outside coders who specialize in building software for Alexa, which the company is betting will be the future of how people interact with their devices—whether using phones or Amazon’s Internet-connected Echo speaker.

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On May 31, developers will no longer be able to submit their apps to Amazon for approval to the Underground Actually Free program. Additionally, Amazon said that people will no longer be able to download free apps that are part of the program to their Android devices starting in the summer, but they could still download free apps if they currently own a Fire tablet.

Fire tablet owners will be able to download any of the currently available free apps until the end of 2019, when Amazon plans to end the program.