Hello everyone. I researches hard for this error and found 0 results. I was watching a tutorial from and in 25:35 time stamp he defines ADamageableActor. Visual Studio gave identifier ADamageableActor is undefined error even though I included and did not make any typo-error. Also this was not Visual Studio error it did not work on Unreal Engine.
Error Message from EU4 log: C:\Users \OneDrive\Belgeler\Unreal Projects\MyProject2\Source\MyProject2\MyCharacterxd.cpp(39) : error C2065: ‘ADamageableActor’: undeclared identifier
if you want more information I asked at StackOverflow link: noredirect=1#comment115746511_65468865 but no one answered so far 
Undeclared Identifier means the compiler doesn’t know what the object is (in this case, ADamageableActor). If you followed that tutorial, you see he creates that actor class around ~20:00, then his project is updated in the background. That can be hit and miss, you may want to refresh your Visual Studio project (you can do that from the File menu in the editor, or just right click on your .uproject and select “Generate Visual Studio Solution”). Then re-open your solution file. If you don’t see “DamageableActor.h/.cpp” - then something went wrong and you need to try again. Once you have that then you should just need to include things and be done.
#include "DamageableActor.h"