Hi mkkc, 

Before sending the invoice, let's make sure that you chose your preferred invoice template on the Customize option. If you want to use this template to all your invoices, you set it as Default. 

Let me show you how:

1. Click the Gear icon and select Custom Form Styles. 
2. Locate the customized Invoice template and under the ACTION column click drop-down arrow. 
3. Then, choose Make default. 
4. Send a sample invoice to yourself to see if it's the correct template used.

    

   

Let me know if you need more help. Have good one!