Plutonium

so me and 2 of my friends wanted to play coop zombies. Only 2 of us have it owned on steam and we searched for a solution to play with the 3rd friend. We all downloaded plutonium, the other 2 ppl connected online regularly could connect to their lobbies. My game side tho f10 menu is loading forever ( message loading... ) when i click online it loads for a long time and then says server is not available at this time and when i click F ingame friends wont show up. Even tried the connect IP address method wouldnt work as well. I searched every single forum believe me every single article and found no solution. Tried the least i found and wouldnt work. Note that i have put exceptions to every single file containted in pluto. Thanks in advance.