Once the Retail Order function is enabled on your system, Retail Order Invoices and Credit notes will follow their own independent document numbering system which can be managed in the 'Documents' area of your system settings.
Click on the cog icon to access your system settings
Head to General Settings > Documents
On the Invoice Tab:
On the Credit Note Tab:
When it comes to reporting, you will be able to filter by e.g. IN/IR only in the IN/CN Number Column:
