Thanks for your reply.
I used the "Enquire More Information" button on this page: https://www.cflsystems.com/remove-branding-for-x-cart-5.html
That opens a pop-up form which asks for name, email, message and an image verification. Filling out the form and clicking "Submit" then leads to the error message about not being able to send the message.
Thanks for letting me know the cost of the module; I assume that would be per domain that I wanted to install it on (looking at four sites currently).