• Find your invoice. 
• Scroll to the invoice you wish to credit. Click Credit Tax in the Actions column.
  
  
  
• Select the checkboxes to indicate whether you wish to credit tax on Hammer, Buyers Premium or Charges or a combination of these.
  Leaving all three checkboxes selected (the default) will mean ALL tax on the invoice is credited.
  
  
  
• Click Credit Tax. A new Credit Note is then created with the appropriate taxes credited.