On a payments queue, you can't lose or double-process a message.
On a payments platform, a message that gets lost or processed twice is real money moving the wrong way. I was responsible for making that reliable under load: catch the bad messages, retry them sensibly, and make sure replaying one can never double-charge anyone. The number I watched most closely was the backlog per partition, because one bad message left unhandled can quietly hold up everything behind it.