Proton-j settle modes

Rafael.

I have simple communication up and running using engine api. When I
send a message by calling send method on Sender object I need to wait
on reply and then I can settle. My communication is asynchronous so I
do not want to wait. I suspect that it is related to the settle modes
that I set on sender and receiver. In my case it is: "unsettled" for
sender and "second" for receiver.

Can you tell me which modes to set and what different modes mean?

Thanks,
Piotr