I think, firstly you have to get acquinted with product listing policy, this information you can find on their page, or the best way is to contact their support team, they will explain the rules and will guide you during the whole process of adding products.
I had the same situation. Firstly, when I saw that my product was blocked, I was extremely surprised, but later I found out that they simply did not correspond to the Company Policy.
I added several products on this platform, but then I noticed that they were blocked. I've contacted Export Portal Team and they said that my products are blocked because there was a signature on items' pictures, so this is not allowed.