Minor fix as to allow to create Invoice from Sales Order when PO is already created from the Sales Order
...
Credit Memo and Refund Functionality
Credit Memo
Create Credit Memo from the Invoice- You can directly create the Credit Memo from the Invoice to which it belongs. Click on Credit Memo Button from the Invoice Page Image Added Select the Line Items and its Quantity for which Credit Memo is required to be created. Then click on create. Image Added Once you click on create, the Credit Memo will be created with the selected Line Items and selected Quantity. The Credit Memo will contain the link for related Invoice and Unapplied amount field amount in this case will be 0 i.e. the same Credit Memo cannot be applied again to any other Invoice.
Image Added The concerned Invoice will show the remaining balance as Invoice Balance against which either a new Credit Memo can be created or Payment can be received. Image Added
Apply Credit Memo to Invoices
Create Credit Memo
Click on Apply Credit Memo to Invoices Button Image Added You will find all the Invoices with outstanding balances to which Credit Memo can be applied Image Added