In this update, I added four major things to SellXP:

1. You can now configure SellXP to modify different parts of its functionality.
2. There's a new function type! The LINEAR function allows you to create worth= cx+C functions.
3. You can now limit when players can sell XP.
4. There's a new update notifer.

Please view the automatically generated SellXP/config.yml file to modify settings.