The information available when you preview the invoice in QuickBooks Self-Employed should be available to your customers also. Let's get this sorted.
To start, send the invoice to your email, then check if the payment details and the message boxes are available at the bottom of the invoice. This process helps determine if this unexpected behavior originates with your QuickBooks or their servers.
If you can see the boxes, this indicates that the issue is not with your QBSE. You can ask them to check if a full cache triggers this behavior.
Here are some troubleshooting steps to get rid of any cache-related issues:
Use a private browser when opening the invoice.
If they can see the payment and message sections on the invoice, let them go back to their regular browser and clear the cache storage.
Otherwise, use a different supported browser.
If you don't see the boxes after sending the invoice to your email, or if they get the same results after trying the steps above, I recommend contacting the Payments Support Team. They have the tools to check your account and investigate this further.
Their office is available from Mondays to Fridays from 5 AM to 7 PM PT and 6 AM to 4 PM PT on Saturdays. Click this link to get their contact details: QuickBooks Payments.
Keep me posted if you need anything else. I'll be happy to help you out.