How do I perform a write-off on a bill?

There are number of ways you can perform a write-off in the application: 

Per proposed value:

When you raise an interim bill on the Billing screen, select the Proposed Bill Amount Basis as Per Proposed Values, and update the billing amount in the Proposed – Fee field. The system prompts if you want to write-off the difference. Clicking OK will automatically write off the adjusted amount. You can view the write-off entry in the Costs screen of the matter. 

Reverse all the outstanding work in progress (WIP) on the matter:

You can reverse the outstanding WIP on the matter from matter Costs > select outstanding WIPs to write off > context menu > Reverse Transactions. 

From Cost Journal Input:

On the required matter, select the Write off/on as the transaction type, and enter a negative amount in the Units. Click Add Transaction and click OK to process the write-off transaction. 

From Bill:

Write-off fees or disbursements from Bill > Review Bill > select Fee or Disbursement, as applicable. Click Apply to process the entry.