I add a reference to the dll file using the OnGeneratedCSProject in Assembly-CSharp.csproj, but unity writes about error CS0246

I add a reference to the dll file using the OnGeneratedCSProject in Assembly-CSharp.csproj, but unity writes about error CS0246: The type or namespace name 'NAME' could not be found (are you missing a using directive or an assembly reference?) What can be done to fix this problem? For Unity to detect the reference? Thanks!