Slitherine

I purchased Empires on Steam and got a 15% discount but paid less than the 25% discount offered? I would like to register the product on Slitherine but did not receive a serial number from Steam. How do I get a serial number?

Cheers
Martin

I am not from Slitherine, but registration is only meant for direct Slitherine customers, as it includes customer service and sometimes specific goodies.