How to install licensed Betheme in multiple sub-domains?

Hi friends! I already bought a BeTheme for Wordpress licence for me and then other for one of my clients. I want to show different demos to other future clients. So I created sub-domians and every time a client accept the design… I buy a new license for them. Now in my company site I found the Register Theme button… with my license no problem. The problem is that when I switch to my sub-domains demo with its own wp installation… if I cannot update many plugins (layer slider, Slider revolution, Visual composer) because all show a small link "Please register the theme"
If I try to register with the same purchase code I guess that it should fine because the license is for one domain… but this are sub-domains.
How can I have many demos to show to my clients to convince them to buy them or me a new BeTheme license?

Thanks!

The licensing system will vary in each theme (some don’t even have license systems). You may wish to seek an answer directly from the author.