Write operations to some third party servers get rejected with the status EnumStatusCode_BadWriteNotSupported
This article is relevant for all .Net products
Not all OPC UA servers support writing timestamps. This is not a bug of the dataFEED OPC UA C++ SDK or the third party server, it is the official way of a server to say, that it does not support writing timestamps. Don't call DataValue::setServerTimestamp() and maybe not even DataValue::setSourceTimestamp() on the DataValue that shall be written, respectively call these methods with an empty DateTime variable to clear existing timestamps.