As some of you may know, Clickbank has recently insisted that vendors ‘inject’ a snippet of code, which renders their banner, on all sales pages. If I add this snippet to the header code box in Customization, then it renders on all pages. It looks like this:
I did quick a Google search and found a guide on how to add a custom javascript into a specific page. You might want to give them a shot. I’d suggest using a Child Theme for this customization. Let us know if it helps.
I’d just like to chime in here. If you’re placing this on the header section I would assume the code goes into the <body> section of the page. If that’s the case, you should be able to just simply place the code inside an HTML module. Does that work?