How can i customize the system email for invoices so the customers PO shows?

Hey there, bryan31. 

I'm happy to show you how to customize your invoice email. Follow these steps below and you'll be able to edit the emails however you desire. 

1. Go to Settings ⚙ and select Custom Form Styles.
2. Under the Actions column, select Edit to change the design on an existing template.
3. From the Design tab, select the desired design you want to apply.
4. Select Done to save your changes.

I'm also going to include this helpful article that highlights the above steps as well as how to Edit Summary or detail invoice emails. 

If there's any other way I can help, feel free to post below. 

Thanks for stopping by and have a nice weekend.