First, go into Xero and find the invoice/credit note. Ensure that this exists correctly.

If the invoice/credit note exists correctly in Xero:

1. Go to Commusoft
   
   
2. Click Settings > Company Settings > Accounting interface 
   
   
3. You will see the accounting interface dashboard. Click View in the failed section
   
   
4. Click on the tab corresponding to the type of record that has failed i.e Invoices/Credit notes
   
   
5. Select the failed record, click Mark as do not send in the top right of this page
   
   

Please note that when you do this you will 'break the link'. This will mean you will need to manually enter any payments related to this invoice/credit note into Xero at a later date