There are a couple of ways to track tip data or other info that may not be set up as a default field in the app.
Option 1 — Change the document type to Restaurant Receipt:
Tap into the receipt details and change the document type to Restaurant Receipt. This will surface tip as a field instead of tax.
Option 2 — Create a custom field:
You can create custom fields in the app settings to track tips or any other data. Custom fields are also included when you export your data.