Where is the best site to sell my used car?

I have a used car that got a fixable issue but it cost more than what I pay for the car, so I am thinking that if I can't fix it, I will sell it. It is drivable, it just an error with the computer, it could be bought for parts or if someone wants to fix it themselves, but I truly only use it maybe once every 2 weeks so for me it's more of a burden.

I have heard of a site called Nettiauto, is that the best site? how much it cost for an ad? if someone can give me some tips also to sell a used car in Finland, much appreciated!