Depends. It can be done misty 5 to backie OR misty 450 to misty 450. So either you are rotating throughout or all of your spinning happens in the first half of the trick.
To the OP, what is your particular issue with the trick? Is there a specific problem you need help fixing? Also, if you have any footage of your attempts, that will make it a lot easier to give you some pertinent tips.
Make sure ur pants are saggy enough so the people around you won't all be staring at the kid going off the big jump. When u eat shit you don't want everyone watching but at least the ones who do see will at least think u knew what u were doing.
if you do it as misty 5 to backy or flat 3, it will be safer to do a flat 3 instead of a backflip. Do a misty 5 and keep taking it another 90° to your back so your landing sideways on the tramp. That will show you the set for the trick. Once youve got that dialed try taking it the full way around.