Slitherine

For a mistake I bought FoG II on Steam instead of Slitherine but after some months, for various reasons, would like to run it outside that platform.
Is it possible?
Is it enough to register it on the member club page?
And, in this case, where do I find the serial number required to register?

Thanks for any hint or tip!

buy from site you get a site key and a steam key, buy from steam or GOG, you just get that version and no other, and can't register here, as not bought from here

Thanks for the sad news ...