R365 automatically uses the settings in System Preferences where GL accounts are assigned to Accounts Payable and Accounts Receivable. When you create AP or AR transactions in the system, the line items to AP/AR are auto-created and work in conjunction with your Aging report. 

To write any transactions to these accounts manually will create an Unassigned Vendor or Unassigned Customer in your Aging report(s). These will not clear until their amounts are removed using AP/AR Invoices, Payments, and Credit Memos, only.