You can choose to turn this feature on if you want your customers to receive separate confirmation emails once they have been charged, not just when they've placed orders.
To turn this feature on, follow these steps:
Go to Settings > General
Scroll down to Catering Settings
Check the box next to Send Final Confirmation Email
Click on Update General Settings
Once you've completed this section:
Click on Email Confirmations
Select Catering Orders and scroll down to Final Confirmation to customize the email
Click on Update Email Settings
You can also choose to send your customers a PDF of the invoice as an attachment to the email by checking the box under the email text.