In Gameplay Modules | Unreal Engine Documentation, section Module Creation. I believe there is a typo in:
[GameName]\Source[ModuleName]\Public
which should be:
[GameName]\Source[ModuleName]\Public
I believe so because there appears later its analog as:
[GameName] \Source\ [ModuleName]\Private
Therefore, it seems that either there is a missing \ in the first one, or an extra one in the second one.