Thank you. After deep investigation, I found that the issue is the shortcode added to iframe do not get rendered:
- when I check the source code in page soruce it looks like as given under:
Additionally, I found that if I change the content template form here:
=> versteckter Link
And try to apply the content template or Layout build with Tooslet it does not get effect. So, your theme looks like taking over the control what to render and discards whatever we set to display with Toolset (content template or layout).
The only way I found to share solution with you is I've added the following code to "Custom Code" section of Toolset:
=> versteckter Link
Question, why you did not use the child themes function.php, to create the short code function?
==> Because if you will change the theme, you need to copy/paste the code to functions.php file again. But as we added the code to custom code section, it will not be the case if you change the theme.