I am an author, I want an explanation on how to get and add purchases keys on my software

[ki-themes]

This one from @baileyherbert should help.

How to verify a purchase code using the Envato API

This is a community guide for authors who want to implement purchase code verification on their items, websites, and applications. If you have any questions or feedback then please feel free to respond directly to this topic.  This topic is a wiki. All active members of the forums can edit it. Don’t hesitate to make corrections or add in any new information. All contributions are welcome! Just want some working code to get started quickly? There are some functi…