Socket Mobile Scanner isn't identifying the barcode with the item

I created an "additional upc" field on the custom tab of items since we have many items with more than one barcode. I then added it to SCIS Website Setup record in the Search Index and as a Field Set for Search. 

This enabled the data in that new field to be searchable when I type in a scan code into Global Search and SCIS search.

However, our barcode scanners (Socket Mobile) aren’t working with this new field. I can see the scanner read the number correctly, but it can’t associate it with a product. It just says “The following barcodes were not found. Please re-scan or search for the items”.  This exact error led me to SuiteAnswer 63935, and I followed it’s direction but the scanner was already configured the way it directed. And, of course, the scanners work with data that’s in the upc field; so I know they work, it's just something wrong with my custom field.