Ask the developers of Insync, UKUU and Aseprite. They sell licences via their sites, with activation codes or Google authentication. But if you want to make a

Ask the developers of Insync, UKUU and Aseprite. They sell licences via their sites, with activation codes or Google authentication. But if you want to make a living, I suggest making a Linux phone oriented application store first and foremost, and figuring out the DRM that way. Developers will come if an ecosystem is built for easy deployments and selling software.