Payment Request default message

I am looking to change the default message for new payment requests, I have customized the “Default” value for the message field in the Payment Request DocType but when I create a new request from a Sales Invoice it still uses the default message template. I should note this is purely for emailing the customer a PDF of the invoice along with some details in the message body, no payment gateway URL or anything.

ERPNext/Frappe Version v13.21.0