I normally wire inserts cable with the tip as send and the ring as return. The sleeve is the common screen.
However, some manufacturers make mixing desks that are wired the other way round, so sometimes I have to swap the mono jacks over.
Think about what happens if they are wrong.
The signal from the desk gets connected to an output on the outboard device, so no signal gets processed. The input from the device gets plugged into the return on the desk.
Thus no signal gets from the desk into the outboard, because there is no connection to the input to the device. No signal gets into the mixer, because there is no output from the device, since it is not receiving anything.
Cheers
Dave