Bumping this because it’s 2023 and this issue still exists with no help from Shopify. Sometimes an invoice gets snagged by customer’s email filters, sometimes it just never gets sent. Also fails to send when I’ve edited an order and customers owe an additional amount. Half the time it works, the other half it doesnt send or gives a red box that says “server error”. Come on Shopify. Completely embarrassing to have to contact customers and find alternative ways to be paid, doesn’t exactly inspire confidence in security for customers either. It’s all fun and games until it costs me money when this is a platform basic that should never fail. Emails/chat/customer service hasn’t ever provided a solution.