Re: I don't get the custom HTML section

Hi @david53

Please, follow the next steps:

  1. Go to Online Store → Edit Code
  2. Appears a new page with a left menu and many folders like: layout, sections, snippets, etc.
  3. Find the folder layout and open the theme.liquid file
  4. From here you need follow the instructions that you put in your question.
  5. Save changes.
  6. Go to your site and the iframe must appears.

Note: These instructions make the iframe appear on all screens of your site. If you need something more customized, feel free to contact me.

Regards.