Why the need for stdcall? Have you tried without it?
Are you compiling in Delphi?
Try a simple example first, such as:
var
CBackProc: Procedure(src: Longword);
procedure test(src: Longword);
begin
WriteLn('Hello')
end;
begin
CBackProc:= Test;
CBackProc(src); // call it
end.
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