Posting to the Chillverse feed isn't available to brand-new accounts — it's a privilege that unlocks once you've been active enough to be a genuine part of the community. To post, you need three things: reaching Gold Rank (or higher), completing at least 150 games in total, and having set a profile picture.
If posting looks locked, opening the composer will show you exactly which of these three you're still missing, so you know precisely what to work on rather than guessing. None of these requirements are things you can pay to skip — they're purely earned through play.