Not a support question, just a quick notice …
I put together a way to convert Scrivener book into Leanpub Markua format: https://github.com/gabr42/ScrivenerToLeanpub
There’s also a book which describes the process. It served as a testbed for my converter: https://leanpub.com/scriv4lean
Both the tooling and the book are completely free, published under Creative Commons Attribution 4.0 International License.
Currently working only under Windows, tested with Scrivener 3.0 beta 17 and beta 18.