There is a bill reversal feature in the Bills tab that allows you to return billed amounts to WIP. Reversing a bill reduces debtors balance by the exact amount of the fee.

Reverse a Bill

Open the Client record or Assignment page for the client or assignment against whom the invoice was posted.

Note: if you want to reverse an invoice created at the client level you will need to open the Client page. If you want to reverse an invoice raised at the assignment level, you can do this through the Client page or Assignment page.

Click the Bills tab, and in the Full Billing History area, select the invoice you want to reverse.
Click the Reverse button and then click Yes in the Bill Reversal message.
Double–click the new draft version of the bill placed in the Draft Bills list.
The Billing Main page opens.
Click the Bill Amount button, .
The Bill Amount page will display and the previously billed amount will now be displayed as a negative amount in the Billed column.
Click OK to reverse the whole amount, or adjust the negative billed amount to the amount to want to reverse before you click OK.
Click the Bill Paragraphs button, .
The Bill Paragraphs page will display and the amount to be reversed will be displayed as a negative amount in the Totals fields.
Click OK on the Bill Paragraphs page.
Click the Submit button , the Authorise button , then the Post button.
Click Yes in the Confirm Posting message to complete the reversal.

Note: you will need the correct level of security to be able to authorise and post the bill.

You can preview or print the invoice from the Bills Ready to Print window, or click Close to exit the window.
Once the screen is refreshed, a new invoice will be listed in the Full Billing History area of the Bills tab once the screen is refreshed showing the reversed amount. The reversed WIP will be available against the relevant assignments when you next bill the client.