I bought EU4 some time ago and recently purchased WoN through Steam as well. Unfortunately, while I have successfully registered WoN on my Paradox account, I cannot seem to register the EU4 basegame for whatever reason despite having tried to do so many times. When selecting EU4 in the 'My Games' tab, entering my CD Key and clicking register, nothing happens at all. This means I cannot access the modding subforum and download a mod from there.
