I have indeed contacted support. Just to follow up:

They have fixed the problem for me, I now see the button to request a steam key at the bottom of my profile page.
Probably there was an error on the website not displaying my steam code because I already had access to the game on steam using Steam ...

Thank you for your quick response. I have not received an email.

A friend of mine also sees a "Send Key" button on his profile page which triggers the email with the steam key to be sent.
As can be seen in the attached screenshot, I do not have this button and hence did not receive the email.

I have done that, but I see no redeem button or whatsoever.

Hello all,

First off I want to congratulate you with this great game you have made! I really enjoy playing it!
I have bought the game on this website, and can play by downloading it.

However I really would like to have it on Steam as well, because it can sync my saved games between desktop and ...