If you are unable to apply the debit notes in your Bills, you will need to check if you have created the Master Debit Notes in the Accounting Tab.
1. Go to the Accounting Tab on the sidebar menu.
2. Select the 'Debit Notes’ card >> Click on ‘Create’ button
3. Fill in the respective field such as the contact name, currency, accounts, tax if applied, and the exact amount to be refunded back to you.
4. Click on the 'Save’ button.
5. Once you have created the master debit note, you can apply them to the respective vendors on the billing page.