Hi, I've been trying to create a post to pomote a sale of my assets but when I try to send it I receive a message "Your post is missing something that the rules require. Please read the rules before posting."

The thing is that I did write a quick description, put the link for the page, an image and a gif and it still accuses error.. what's wrong?

Make sure the link to the project page is correct, and that the page in question is public. Otherwise I'm not sure.