Hmm… haven’t ever really done one on a slappy but I’d imagine its not much different from a flat bar.
When i krook transfer, I jump into it normally and as soon as I lock in I start putting more weight to my front foot which starts to tilt the board more upwards. Get your leading hip over the obstacle and if you’re stable in that position the transfer should come pretty easy with just a slight nollie out.
You don’t need to pop very much, rather use your body’s momentum to bring it over.