How to correct this distance error???

[wuxuechen]

In this instance, pressing the full screen button will eliminate the sub windowSub-Application.jpg

[wuxuechen]

When resizing a window, the child windows do not follow the zoom and are not positioned correctly222 (2).jpg

[defisym]

In this instance, pressing the full screen button will eliminate the sub window

Make sure you are using the newest version.

When resizing a window, the child windows do not follow the zoom and are not positioned correctly

Gosh.....
I can't do everything for you, you cannot make anything by just copy-pasting someone's code.
It's quite easy to implement this: save the old frame rectangle size (IIRC I made a expression for this, in window->get rect), and re-check it in an always event. when it changes, then update the position/size of sub-application with the new frame scale.

[wuxuechen]

The latest version 293.6 is used

[defisym]

The latest version 293.6 is used

the newest version of EXTENSION. IIRC there is a bug when getting frame scale Y. I will post it here, hope it will solve your issue.
WinAPI_210826.zip