1. Navigate to Billing > AR Ledger.
2. Click on the 1st tab: AR Ledger - Claim Wise. 
3. As you generate the table using filters, click on the box under the Action column.
4. Add required comments under the Claim History section. 

All the added comments to the claim are available in the claim history screen along with the time stamp. To add a new comment, enter it in the text box and click the Add Comment button.