AX 2012 - Create Credit Note Issue - Unable to "Select All" Invoices


I am trying to CREATE a CREDIT NOTE behind an Invoiced Sales Order and when I select the Order > Go to ‘Sell’ on the action pane > Create Credit Note, I am unable to select All / any invoice for Credit Note creation (check boxes greyed out). What’s the show stopper here please? Interested in specifically creating a CN via this process and not via Return Order or FTC etc.

Thank you all

Quick Clarification - I can follow the route to create a NEW sales order, then click on ‘Sell’ > Credit Note and pick up an invoiced order for the customer in question. My query is whether & how to create a credit note by directly picking up a Sales Order that has been invoiced. Idea is to have the original invoice and CN all in one place / linked / associated / referenced. Would not creating a ‘Sales Credit Order’ orphan it from the Original Sales Order?