Embed control from dynamic library into groupbox

[7bit]

I have a control in a dynamic library that I want to embed in my application, or rather in a groupbox. I'm using the ShowMyControl library function, which takes a handle groupbox as a parameter. In the library itself, the ShowMyControl function creates a control and places it in the parent using the ParentWindow property. But as a result, instead of embedding the control in the groupbox, a separate window is displayed. Although if you do the same with the application control, everything works as it should. Can you tell me how to solve this problem? I am attaching examples of a dynamic library and an application for testing the library. In the startup parameters in the Environment tab, set your value to the LD_LIBRARY_PATH variable.

Lazarus 4.3 (rev lazarus_4_2-26-g44b59001af) FPC 3.2.3 x86_64-linux-qt5