Error suggests that compiler can’t find the definition of TheStruct::Func1()
I just found out that if you create .cpp from Visual Studio, the default path will point to “Intermediate”. Since you’re using a separated .cpp file I’d suggest you checking the path of TheStruct.cpp and make sure it’s under Source/[ProjectName]
If this is not the issue, try moving the function definition into TheStruct block first. I know it’s not ideal but you need to narrow down the issue.