26 days ago - Shurenai - Direct link
No epic account is needed. But the game does connect to Epic Online Services for multiplayer stuff, and generates a unique token when doing so; Failure to get this token would likely result in the error you're seeing.

If at any point in the past you ever blanket blocked all EOS/EAC/Epic services because you hate Epic and all they stand for and refuse to let them have any access to your computer; Having done so would make it so the client can't reach EOS, and would cause problems.

There may be other causes for it too, but I'm not personally aware of any.

As far as fixes go, If you don't care about multiplayer, there is a fix of sorts that may help you. In the main game folder "...\steamapps\common\7 Days To Die", there's a file named "platform.cfg"; edit this file and on the second line remove the "EOS" that follows the equals sign.

Should end up looking like this:

Save it, and launch the game.