ProudDotNetClient.dll shouldn't be in Asset Folder(Unity 4.xxx)
Follow 3. Unity plugin file import
order. (ProudDotNetClient.dll instead of ProudDotNetClient - iOS.dll)
Menu - File - Build Settings - Select Platform(iOS) and configure Player Settings
Menu File - Build Setttings - Other Settings-Configuration. Set Scripting Backend to IL2CPP
Menu File - Build Setttings - Other Settings-Configuration. Set Target IOS Version above 5.1.1
In order to build XCode project generated by IL2CPP, Include "*.h" files in "Proud/include" folder into XCode project.
Copy "Proud/include/*.h" to generated XCode project's Libraries folder.
Generated XCode project Build Settings - Search Paths - Header Search Path. Put "Proud/include" folder as relative or absolute path.
Open XCode project generated by IL2CPP Build
Unity 5.x
XCode - Build Settings - Other Linker Flags. Put "-force_load $(SRCROOT)/Libraries/Plugins/IOS/libProudNetClientPlugin.a"
XCode - Build Settings - Apple LLVM 7.0 - Language - Object C. Set C++ Language Dialect = C++11, C++ Standard Library = libc++(LLVM C++ standard library with C++11 support)
XCode - Build Settings - Architectures - Other. Check arm64 only.
ProudNetClientPlugin_wrap.cxx file might not exist in generated XCode project. If not, Copy "ProudNet\lib\Plugins\Unity\5.x\IOS\ProudNetClientPlugin_wrap.cxx" to "XCode Project Path\Libraries\Plugins\IOS\"
XCode Menu - Product Build or Run.