The following procedure shows how to print a barcode on receipts that will be used as access pass (sold via Proshop).
1) The first thing to be checked is whether the white list for the creation of barcodes is enabled: Settings -> General Settings -> White List -> Enable White List. You can find more info about the white list here
2) CREATE DOCUMENT NUMERATOR: please refer to Document Numerators
3) CREATE DOCUMENT TEMPLATE FOR THE RECEIPT: click on Settings -> Document Templates-> Add Document Template -> select 80mm -> click on OK -> click on Edit and specify:
name
numerator
enable the "Visible" option
enable the "Print Receipt" option
click on Devices and select the cash-register the receipt will be printed from
save
4) SET UP THE AUTOMATIC PRINT OF THE DOCUMENT FOR PROSHOP SALES: Click on Settings -> General Settings -> Documents -> set the document template you have created as default document for Proshop
5) CREATE TAX: click on Settings -> Tax -> click on Add to create the tax that will be linked with the items sold via Proshop ->click on Advanced Management and click on Edit next to the tax you have just created 
select the tax from the menu
specify whether the tax is to be included in the sale price of the item
select the document template in the STANDARD field to automatically print it every time an item linked with this tax is sold via Proshop
click on Add
click on Save Changes
6) CREATE PROSHOP ITEMS: click on Planning -> Proshop and create the necessary items (see Proshop - Items).
Please note that it is necessary to enable the option shown in the picture below to print the barcode on the receipt. Just click on Edit next to the Proshop item and then click on More
Important: on each receipt there can be just one barcode valid as access pass. Therefore two passes = two items sold = two receipts = two barcodes.