At least you asked. I wasn't thinking and wired it backwards (line-in to terminals on the bottom of the breaker and the load cord to my panel off of the spa panel lugs.
Somehow it all worked but when I went to test the GFCI, I fried it and let out the magic smoke...
Once I wired it up correctly the same breaker functions but not as GFCI. Now I need to figure out if I want to replace the breaker or just get another spa panel.