You must export your v3 vouchers using /vouchers export before updating, then use /vouchers import in v4. A lot has changed setting/usage wise so please test a non production server first. I'm currently rewriting the docs. Please join the discord for help if you run into any issues.
+ V4 is a 'hybrid' between using the in-game and file editing methods, changes done to the file will automatically be reflected in game, as with changes in game, those will be updated in the file right away. If you have questions on how to use it please leave a message in the appropriate channel in the support discord.