It all depends on which version you buy.
If you buy OneBox MVP or older, then you will have to upgrade to OneBox OS for money, only after that all functions will become available to you. The transition is optional: if you are satisfied with the version that you buy, then you can stay on it. Although officially from January 1, 2023 MVP and earlier versions are not supported, that is, you will not be able to present any claims to OneBox.
If you buy OneBox OS, then all functions will be available to you.
Version history here -
https://1b.app/ru/version/The official announcement about the end of MVP is here -
https://1b.app/ua/forum/onebox-official-news/14157-ofitsiyno-kinets-pidtrimki-on...---
In addition, I want to note that it all depends on the purpose of your purchase:
Option 1 - if you buy a customized system for some business and it is configured for MVP versions - then okay, this makes sense, because earlier another person configured it, invested money in it and sells it. In fact, you are not buying OneBox, but business settings. In this option, if you want OneBox OS, you will have to upgrade for money, and they are equal to buying OneBox OS from scratch. But most likely you won't have to pay anything for the settings.
Option 2 - if you just want to save money, for example by paying only once.
There is a place to be, but you will stay on the MVP, because OneBox OS is available only by subscription.