HoloLens cannot connect to OpcUa server

I want to connect to the OpcUa server through the APP on HoloLens and read the node's data. It works on Unity Editor, but it can't connect to the OpcUa server in HoloLens. I use the OpcUaHelper plugin, which has a simple OpcUa client and supports .Net Standard 2.0. I imported the dll files for opcua into the project folder (Asset/Plugins/).

Maybe I used the wrong dll file version? Which version of the dll file should I use (.net standard 2.0? or .net 4.6.1?)

Does anyone know what the reason is? Or have anyone tried to connect the Opc Ua server in HoloLens?


Unity's settings are:

Scripting Runtime Version: .Net 4.X Equivalent

Scripting Backend: IL2CPP

Api Compatibility Level : .Net Standard 2.0

The version of the software I am using is:

1.Unity 2018 3.11f

2.Mixed Reality Toolkit v2.0.0 RC1

3.Visual Studio 2017