It's easy to edit the session fee.
If you have already created the invoice, first delete the invoice if you want to change the session fee so this way you don't have multiple invoices and adjustment invoices.
1. Navigate to the client's billing page.
2. Hover over the session that you want to change the fee for.
If you have an invoice for the session, you'll see that listed in the same line as the session in a blue outlined box. Click on that to open it and delete the invoice before changing the session fee.
3. Click on the Edit link under the session dollar amount. If you don't see the Edit button appear, that means you have a Superbill attached to that session. You'll have to delete the Superbill before you're able to edit the session fee.
4. You can now change the session fee to the dollar amount you would like to bill the client.
If you normally charge a set fee but are charging a different fee for this single session, you can add the write off amount to make the difference (for example if you normally charge $100 but this time you are only charging $60 for the session, you can add a write off of $40 and leave the session fee as $100)
5. Click Save.
6. Now you can recreate the invoice.
If there are multiple sessions to be invoiced but you want them on separate invoices, just change the date range to only include the session you would like to invoice.