QoS 1

Deliver once - I don't care if you send it 10 times, just make sure they get it.

QoS 1 is the most commonly used level. It guarantees the message is delivered at least once. Duplicate messages need to be handled either on the subscriber side or in some post processing. There is a higher communication overhead than QoS 0 but only half as much back and forth as QoS 2.

QoS 1 is used when delivery needs to be guaranteed and the use case can handle duplicate messages.