You have just read some data from your OPC UA server, from a node that is supposed to contain useful, structured information. But all that you got is a seemingly undecipherable array of bytes, in a form of an extension object. What has happened?
Well, you have met a custom data type (UDT), defined using OPC UA Complex Data. The encoded data indeed contains the requested information. But you need to decode it, using information contained in a type dictionary within the server. Or, when you are writing such data into the server, you need to encode it, according precisely to the rules. And you need to navigate the information model in order to put together all the pieces necessary to look up the type dictionary and the specific definition inside it.
And there is no support for that in the stack and SDK from OPC Foundation.... What to do now?