If you need to remove a billable item on the invoice but that item is locked we can reverse payments to unlock the item (Note this only works for manual payment types, 3rd party integrations usually have their own set of rules).

Firstly refund any payments and reverse discounts associated with that invoice, this will revert the invoice to unpaid, from there you can modify items on the invoice.

Below is the step-by-step process on how to do it.

Step 1: Open the Invoice and select Refund.

Step 2: Select the Payment and enter the Amount, Payment Method, and Click Issue Refund.

Once refund is processed, you can check the invoice on the unpaid tab.

After doing a refund and reversing all payments and discounts you will be able to amend any item codes and recreate the payments

Additional Resources: How to Refund a manual payment