How do you take a credit off of an invoice that was meant as a tip and not part of the actual charge?

Good question, deannaandes.

You can edit the invoice, creating a new invoice for just this tip, or creating an invoice including the tip amount. Before doing so, make sure to create an account to use for your tips

Here's how:

1. Go to the Gear icon, then choose Account and Settings.
2. Select Advanced.
3. Go to the Chart of Accounts section. Then select the pencil icon.
4. From the drop-down, choose your desired account for tips.
5. Select Save.

Once done, you want to set up a Product/Service called Tip. Then, apply it as another line item in your invoice.

You can do this by following the steps below:

1. Go to the Gear con, and then select Product and Services.
2. Select the New button.
3. Choose Service.
4. Input all necessary information of the service.
5. Once done, click the Save and close button.

For additional information, you can go refer this article: Add tips to Sales Receipts.

You may also want to run the Total Pay report to help you see the cash tips. Since the report shows the total pay by pay type, you can export it to excel, then customize it to show only the cash tips total.

Here's how:

1. On the left pane, select the Reports menu. 
2. In the Find report by name field, enter and select Total Pay.
3. Filter the report to show your desired date range and work location, then hit Run Report. 

Drop me a reply if I can help you with anything else. Hope you have a good one.