Under 'CRM,' select 'Vendors.'

Select the vendor you want to raise the credit for and either double click on it or click the triangle

Select the financial tab in the change supplier screen and check 'Invoice ok without Purchase Order.'

Go  back to your main menu and select 'Purchase Invoices' under 'Invoices & Payables.'

Select the vendor you wish to create the credit for and click '+ New Credit Note.'

Select the relevent supplier using the first magnifying glass then click the plus in the bottom right corner to add the unrelated credit.

Double click on the amount filed and add the amount - you can also add a description and change the tax code in the same way.

Add a credit note number and relevent dates and payment methods. Then click to create your credit note.

The credit note will now appear in the list.