Hi Paul,
Try this: Pass the entire received contents from the Socket Agent notification to MII, and then use the MII Advanced Flat File Parser to split the string on the '~' character. This should give you an MII Rowset output, with one Row and two columns; used the 2nd column value for the barcode you need. Advanced Flat File parser is standard with MII14 and later and is available as a custom action block for MII12.2 and earlier.
Regards, Steve