The 3.x version of the plugin is not backwards compatible with 2.x.
3.x uses an entirely different code base and design approach, and as such, the two plugins cannot be migrated. This means 3.x should be viewed as a completely new installation and requires set-up for every product you currently have configured for 2.x. Furthermore, we recommend familiarising yourself with how 3.x is configured and carefully reading the documentation.
We highly recommend backing up your current site and testing your installation thoroughly, preferably on a sandbox or testing site, before transitioning to a 3.x install on your main site.
While it can be possible to run 2.x and 3.x at the same time, we recommend not doing so unless absolutely necessary. If they are run together, this should only be for a short period of time to complete your transition.
We do not recommend new installations of 2.x as support will end one year after the release of 3.x.