Freelancer attending a conference in Germany, what type of visa and what documents are needed?

I work as a freelancer and I earn a lot of money, but I do not have official government documents because the freelance activity has not legalized the title here in Morocco .

I just got a ticket for WordCamp Europe 2019 with an invitation letter. Now I want to apply for a visa but I'm not sure how to address it, I've visited their website and there are specific documents for each job, but mine is not not included. So, my question is:

  • What type of visa should I apply for?
  • What documents do I need for my application to be approved?
  • Do I even have a chance?