You don't necessarily have to send invoices to your customers in separate emails. Instead, your online store can include links to view, download, print, or pay your invoices online.
There are different ways you can link to your Sufio invoices:
Add links to invoices in the Order Confirmation emails sent by Shopify.
Insert links to invoices on the Shopify customer account page.
Link to an invoice on the final page of the Shopify store checkout.
Add links to your invoices in the automatic emails sent by Klaviyo.
Add links to your invoices to your automatated emails sent by Omnisend.