How do I sell licenses for my own software?

1. Open Plugins > Add New, install Sell License and activate it. A License menu appears.
2. Under License > Software click Create and add your software (name, slug, and a version with its zip on the Versions tab).
3. In Products & Pricing create a product of the type Software License. Under Module Settings > License Settings choose the Key Prefix, the License Type (One Time or Monthly / Annually) and the Software Identifier.
4. When an order is paid, a key is created for the client automatically. They see it on their service in the client area.
5. Under License > Licenses click Download Client and put LicenseClient.php in your software so it checks the key before it runs.

The full guide: Sell licenses for your own software.