Question: 

When making a credit note, how can I refund only the charge line?

Answer: 

When creating a credit note, there must be at least one product line added to be able to process the credit. 

Should you wish to process a credit note for just the charge line, simply make your "Credit Qty" and "Credit Price" to be 0 and the system will only add the charge line price to your overall credit amount. 

​​