I am using the .NET SDK for creating email campaigns, but when I save it with the country set to "MX" the campaign preview (and the email sent) shows "null" in the footer. I made tests with the API tester and it's the same. Please contact me if any further information is needed.
We are aware of this issue and working toward a resolution. Currently the work around requires you to log in to the website and edit the email in question, then click the Message Footer link, then click the Preview and Test button. This will populate the Country Field.