Hi UserCleanedbyClaires, 

Thank you for getting back to us on this and I am sorry that's how you feel. 

I tried following AileneA's instructions and I was able to find the customise button on my invoice in my QBSE test file to edit the email message. 

I would suggest contacting our QBSE support team for additional assistance if you are still experiencing difficulties in doing so. Here is their contact detail:

https://help.quickbooks.intuit.com/en_AU/contact

Thank you and please let us know if you require any additional assistance.