Hi, first of all thanks for your using Cosmos WordPress theme. Yes this issue was noticed from our another Hostgator users. The problem source is Hostgator is prevent our private repository, when attempt to during necessary plugins install. You need to contact Hostgator and send our IP to allowed list.
You can check your email we’ve send our ip’s to your inbox. As alternative solution please let us know your login info to our support team info at themeofwp.com. Our support team will be install all plugins for you.