In „Billing” Module you select the subcategory „Configuration”.
In the middle part you will find more fields to complete with your data. The name of the company which is going to make the payment, The Unique Registration Code/Fiscal Code needed to issue the invoice, the name of the bank that will process the payment, IBAN code of the payer, the prefix of the array from the invoice (it can be set depending on your preferences), the number of the invoice (from where the billing starts), the day of emission of the invoice and the days until due day for an already issued invoice. Press „Save” button and automatically save the billing data.