It was a bit sketchy. After the presale started, the Nashville page accessed by the link in the presale text message did not show tickets, it was the same page as before the presale started. I then checked the Chicago page and it showed tickets. I kept trying Nashville, refreshing the page, I cleared/deleted Ticketmaster cookies, I searched for U2 from the generic Ticketmaster site instead of using the link in the presale text message, etc. I finally got a Nashville page that prompted me for my presale code and from then on it was smooth.
I'm not sure what the key was