[Koha] Barcode not found - Show matching titles

[John J. English]

Hello, I'm trying configure my Koha instance so that can process a checkout on books that do not have barcodes associated with them. 

I've tried enabling <itemBarcodeFallbackSearch> but it isn't working. 
When I click "Show matching titles" I get an empty model that says: Barcode not found. The following items were found by searching:
There's nothing in the model, even though I know the book is in the catalog. 
I've tried reindexing Zebra, but it didn't help. 
Any advice is very much appreciated. Thank you.  

JOHN J. ENGLISH