Follow the steps below to credit an invoice:
Go to Back Office (blue module) > Invoicing > Invoices
Find the invoice you want to credit. You can use any of the fields below to find the invoice
Mark the invoice and click on "Credit"
If you want to both credit the invoice and cancel the booking - leave both boxes marked. If you want to only credit the invoice but not cancel the booking - unmark the box under "Cancel". Make sure the "Credit the original invoice" box is marked.