Airport trip from Munich

Buyer Beware! Googled ahead to make sure I buy the right ticket. Had a Day ticket that straddled during my trip to airport. Bought one online and the other at the airport. Bought a connecting ticket to Zone 5. Went my merry way to train. Random ticket check but thought I did it all right. Checked my ticket and she said I needed to buy Zone 1-4. You would think the machine would have done that. Paid my 60 euros penalty right then and there and she said I now have an unused ticket I can get reimbursed. I also needed to stamp it. Lesson learned: buy online as it is smarter. Not required to validate. Almost every Reddit entry issue comes from those buying at station.