First and foremost, you will need to identify what kind of barcode your client's POS is using. Here are the barcodes that are currently supported:
Code 2 of 5 interleaved
There are several ways you can create a barcode.
1. You can have the same barcode for everyone.
2. Or you can have a personalized barcode if you import the barcode value into a merge field. Then you select the field you are using and place that in the barcode field by selecting the Insert Field option. This will pull all of your merge fields, and you would want to select the field that contains the contact's personal barcode value.