How to modify Negotiation "Online Message" Email Notification Template

Summary

Looking to add additional wording into the "Online Message" Email Notification Template

Content

Hello,

I am looking to see if it is possible to add some additional wording into the "Online Message" Email Notification Template?

I want to add text along the lines of "Do not reply directly to this email, log into Supplier Portal to reply to the Online Message".

I have looked in the BPM setup for the task = OnlineMsgNotifFyi - but couldn't work out if I can modify the template?

There was something under Notifications > Notification Header where you can add some text but when I tested it the email notification said "Notification header is not included due to incorrect expression in the setup". I don't know how to write an expression for this.