If your're talking about the "MP3 Converter for Studio One Artist", you might want to read the product page. It says there; "Will work with all Version 3 builds." MP3-Encoding/Decoding is now included in all Studio One versions.
https://shop.presonus.com/MP3-Converter-for-Studio-One-Artist
https://www.presonus.com/products/Studio-One/compare-versions