Just bumping this in the hopes that someone is reading.  Problem remains:

The Message on an invoice template doesn't show up when an invoice is actually generated.  Other changes show up, but not this one.

We'd want to make sure all details are showing up when the transaction is generated, crewjoy.

I also wanted to ask what have steps you tried so far? Have you created a new template to check if the message would show up. I'm asking these questions because the investigation that was previously mentioned in the old responses has already been closed and resolved. This is to also test if the template you're currently using is the one that's having the issue.

If you haven't tried it yet, follow these steps on how to create a new template:

1. Go to the Gear icon and select Custom form styles. 
2. Click New style in the upper-right hand corner and select Invoice.
3. Proceed to the Content tab and click on the pencils (you’ll see them in white) in the right-hand corner. 
4. Scroll-down to the Message to customer on section and type in your message.
5. Click Done to save the changes. 

After that, create a new invoice and print it to check if the message is now showing up. 

I'd also like to share a couple more articles about customizing sales forms in case you might be interested in using them: 

• Add, Customize, or Remove Logos on Sales Forms 
• Customize Invoices, Estimates, and Sales Receipts in QuickBooks Online 

Don't hesitate to share updates and let me know if the message is now showing up. You can also reach out to us again if you need anything else. 

It won't update existing invoices but will update all new invoices.

Just go back over your open invoices and paste in the customer message and save.

The message will automatically appear even in the invoice on screen for all new invoices but won't retrospectively do this for existing invoices.

Using the Customer Message field is not a template change as such, it literally fills in the detail to the Customer Message field on the actual invoice. 

Thank you Nathanel !!

You nailed it! 

I didn't want to be stuck with a list of new invoices creating the same issue, so I kept checking back to my last saved invoice where this problem with the message arose.  

After reading your answer it made sense and I courageously went ahead and made up a new invoice, saved, and Previewed - Voilà! -it was good.   

I hope all the other users have seen  your answer. 

Well, that is frustrating that I can't change all my current open invoices (100+) and have to create new ones to relay important information and change the current message that is on the existing one! I've spent the last two days about to pull my hair out trying to change this, only to find this thread saying I have to start over! QuickBooks is great. However...there are too many limits on things that I want to customize! My company is a concrete/gravel pit offering products to homeowners and contractors. So - of course, we offer our contractors different billing periods and better rates than the average "Joe" but there really doesn't seem to be a way to categorize them into different groups, and then have a set template for contractors vs. homeowners. The statement options are also horrible! The online payment option is per individual invoice, not by monthly statement. If anyone has suggestions on any of this....PLEASE let me know! 

I wanted to chime in here, hoping to save a newbie out there (like me) some frustration. We couldn't figure out why, after changing the invoice template, the custom message showed on the preview but not on the actual invoices.

It turns out, we have to add this manually (copy & paste) to all our existing invoices.  Once the invoice is in the system, it doesn't pull new content changes from the template.  Because we invoice our customers weekly and normally duplicate the previous invoice, make the necessary changes, and save the current week's invoice, this would never show up.  New invoices, 'started from scratch', would bring in the new verbiage.

Hope this makes sense and helps someone else!