Ah, the lessons of Sensei Pain are swift and memorable ... tho', considering you've done it three times now, I think perhaps he's getting soft :lol:.
Seriously, what's going 'wrong' with the technique that you're hurting yourself?
Is it timing? Angle of the foot? Specific target?
I'm just shooting out inane questions into the dark in the hope that, as you answer my know-nothingness, a solution will come to you :tup:.