Problems happen.
The Simple Answer
There might be an attendant nearby to help you, but don’t count on it. Keep a second way to pay (second Breeze Card, mobile app, or ticket).
The More Complicated Answer
If you’re inside the station gates and can’t get out, there’s a phone nearby to talk to an attendant. I’ve never used it myself, so I’m not even sure who it rings. Tailgating on the way out, though not really encouraged, is common (for definitions of the word). You already paid your fare so you’re not stealing any services.
If you’re outside the station gates and can’t get in, you’ll need to find an attendant to help. If you’re at Airport or Five Points Station, there’s a RideStore location where you can get help Monday through Friday from 8am to 5pm (though I’ve never found the one in Five Points). There are people at the parking booths at the long-term parking lots, but they can’t help you with passes or the gates. Don’t tailgate to get into the station; you should pay your fare like everyone else.
If your card doesn’t work getting on a bus, you’ll need either $2.50 in cash or the phone app (or a second Breeze Card). The driver often will just wave you on if you’re at a station since you’ve already paid your fare.
I suggest having a second way to pay for a ride on you. I have about $10 on my Breeze Card app at all times in case I have issues with my card.
The Details
MARTA does have a customer service line to call if you need help. See this page on MARTA’s website for that number. Note that the hours as of March 2024 are Monday – Friday from 8am to 5pm. This won’t help too much if you’re a weekend travel like I am.
During big events, there are attendants everywhere at the stations making sure people can get in and out. On the day of the SEC Championship game this year, we wound up at the East Lake Station where I have never seen a single attendant before; there were two at each gate and two at the top of the escalators that day.
I wouldn’t rely on social media to contact MARTA for help. They’re not going to respond to you quickly.
Did I mention that you should have a second way to pay on you just in case? You can buy a paper ticket as a backup, but be aware that those expire after 90 days. Cash on a Breeze Card is available until the card expired (three years after purchase). Cash on the Breeze Card app should be available indefinitely.