How can I add Shopify orders to a customer's monthly invoice instead of it becoming a sales receipt.

Good day, EB2018.
 

I want to make sure you get the best help possible. As a default, once you integrate QuickBooks and Shopify together, orders will be exported as sales receipts. However, you'll want to contact the Shopify Support and request to add orders to invoice instead of sales receipt.

You can reach them through this link: https://docs.shopify.com/support

I'm leaving this article to learn more about how Shopify works with QuickBooks Online: Shopify for QuickBooks Online.

If there's anything else that I can help you with, please let me know in the comment section below. I'm always around to help.