I have seen a lot of threads lately asking about boing-e-boing, and i just mastered it recently (completing every thing in the YYE trick list!) and here is a couple things that helped me:
1: IT’S A UP AND DOWN MOTION, NOT A SIDE TO SIDE!!
2: doing a few barrel rolls first can make it easier for you to land the trick (less having to make sure your not gonna miss the string so you can concentrate on the motion)
3: Learning Boomerang helped my boing-e-boing pursuit immensely
4: If technique “1” didn’t work out for you you can concentrate on the motion of it by not putting the yoyo in a split bottom mount, just pinch the string close-ish to the yoyo and start trying the motion.
5: At the top of the split bottom mount, instead of letting the yoyo slide across your throw-hand, pinch the string, that really helped me get it down for some reason
6: I practiced the motion with a rubber band, kinda weird, but it really helped me get the feeling for the trick down.
As the wise Ed Haponik once said, Legit boings take years to master, some people are born with a “boing” jean, some arent, and just need to practice more. ( i think it was something like that)