Quick question for web devs

So I have a small problem that is probably easy to solve so I thought some of you guys know how to do it.
I would like to implement a Gumroad link on custom button with overlay using theSeven theme, so that this custom link can generate an overlay right there on the site. Instead of this overlay I keep getting forwarded outside of my site.

Here is more info about that:https://gumroad.helpjuice.com/how-do-i-set-up-the-gumroad-overlay


I used RawHtml fro Visal composer for the script part.

Any ideas how to make this work?