One of the methods that other 3rd party apps will use to load their content onto your store is with an iFrame element.
Sometimes, the element does not appear inside the visual editor. This is the most common problem with iFrame elements. It can be solved by sending us the translation data, so we can input the Visual Editor style translations manually from our end.
However, this is not possible if the iFrame is loaded from a different domain. You can tell an iFrame is loaded from an external source if it has an "src" element when you inspect the element in the browser development tools, and it is not from the same domain as your store. In the following picture, an iFrame element from an email app has an "src" element. The domain in that element is form the app, and not the domain of the store, meaning that the iFrame is loaded from a separate domain.
When the iFrame is loaded form a separate source our app is not able to modify it in any way. This is a limitation that is put in place by all modern Web Browsers for security reasons.
We can translate iFrame elements that are from the same domain as your store, even if they do not appear in the visual editor. Please contact us at email@example.com to assist you with this. However, if the iFrame has an external source, then we are not able to modify it to apply our translation data.