I tested my payment process by adding products to a cart and going through the checkout process. However, when I get the email notifying me of the transaction, it shows the localhost URL as in the image below:

Is there a setting I am missing in Heroku? Thanks in advance.
You need to change the site's domain in the dashboard site settings. That should fix it.
Thanks @NyanKiyoshi you the best!
Most helpful comment
You need to change the site's domain in the dashboard site settings. That should fix it.