It says i dont own the base game even though i do - therefore unable to enter. With zero entries after 1 day, other people are having the same issue too.

i dont know sorry whether support can help.
for another giveaway, the person gave the key away still based on asking people to leave a "yes" comment and he picked someone at random.

I have the same problem and as someone said previsouly, it is happening for many games or DLCs. :/
Yes it could be nice to give it in another way if you feel confortable about it!