Saw this offer and bought it without thinking, but now i realized that maybe this was not intended.
It's not a bug. On rare occasions, the Rumble shop offers a 5* Child ticket, 5* Soul Carta ticket or 5A equipment ticket for 777 coins. It's a luck thing.https://moot.us/lounges/73/boards/289/posts/2793395/finally-got-my-first-777-5-child-ticket
This is very rare offer in rumble shop =) I got around 10 from ~3 years of play(most on 1-st year when i wasn't lazy to check it every 3 hours xD)
Once my luck was so bad I filed a report in this section. This is different.
this is not a bug