I don’t have that much experience with scanning barcodes, but I believe it’s an action itself, so you can’t add branches of logic after that action, in a custom action chain, as of now.
I believe what you can do for now is:
- Add a button to scan the barcode and write it to a column.
- Use a relation to determine if the barcode has been added or not. If added, show a hint that it has been added. If not, show a button to add a new row with that code.
That should be done in a custom form environment.