You don't necessarily need to send invoices to your customers in separate emails. Instead, your online store can include links to invoices for your customers to view, download, print or pay online.
There are three different ways you can link to your Sufio invoices:
Order confirmation email
Add links to invoices in the Order Confirmation emails sent by Shopify.
Customer account page
Put links to invoices on the Shopify customer account page.
Order status page
Link to an invoice on the last page of the Shopify store checkout.
Beautiful invoices for Shopify stores
Let Sufio automatically create and send beautiful invoices for every order in your store.
Install Sufio - Automatic Invoices from the Shopify App Store