OPC UA uses StatusCodes to identify the success of operations, including Method calls. However, StatusCodes cannot be extended, and often it is desirable to receive a more detailed application-specific, program-readable reason, why a Method call was not successful.

The following pattern should be used to return application-specific statuses of a Method. The last argument of the output arguments of a Method should contain an application-specific error code. The DataType should be an Integer, preferably an Int32. The information model might provide a description of the values in the Method metadata.

In the following, an example of such a Method definition is given, using the template for Companion Specifications.