Comment 25 for bug 1798187

+1 to having a pop-out help. You should be able to add one with the following code in the tt2 file:

 <eg-help-popover help-text="[% l('Barcodes should not contain spaces') %]">

And you can replace the text within l('') with the guidance you'd like to give to the user.

Also, +1 to reporting back on which barcodes failed to load, and for it to be less intrusive than the XUL popups.