Mobile app for codecanyon script

recently I can across imo a very good codecanyon website system. I would like to create an android app (frontend, backend api, ui) for the script and sell the mobile app on envato.
I contacted the support and he claimed that there would be copyright issue (infringe on the original author’s rights) as I would have to reference the website system on my product description page.

Now, my app will only work if the buyers have this website system already purchased. I don’t know why I would require permission from the author of the website system. Do theme developers require permission to develop themes for websites ? so anyways I contacted the author and he doesn’t want me to sell any app for his website. My plan isn’t to sell the app using any copyright names or scripts. I would be using my own app name.

I need some actual guidance on this one.

There’re some items are based on another scripts on CodeCanyon such as Visual Composer add-ons.
What you need to clarify is to make sure the buyer sees the information that they have to purchase the original item apart from yours and give the original link to the item.

This shouldn’t be a problem as long as you don’t use any material from the “original script” but at some point, you may have to deal with copyright claims.