Very frustrating when this should be the default… adding a copy of an invoice note, after sending to a customer, to display on the timeline on orders/draft orders.
If sending just a message from the order page, it will save this to the timeline with a dropdown to view… but for invoices, nothing except having to CC an email address, which is easily missed.
Once sent there is no way to retrieve the message, which is insane. Closing a deal without context to refer back to is utterly ridiculous to not be the default. Fix it Shopify.