I've been using the software for over a year, so I know what I'm talking about. Yes, there are sometimes problems with posting content, but generally, this has to do with the proxy behind it that is flagged on the IG API (used by GMT). By testing different proxies and creating an account the correct way, you shouldn't have any problems posting content. What you can also do, if you have problems posting photos, is to post videos for a while first, this will also help sometimes.
It is for a reason a sales page; if you have problems you need to report it via a support ticket. If you don't agree with that, it's annoying, but it won't change soon.