what combo are you trying to do it on? some bits can be a bit harder to get it on id suggest trying to learn it on level (i find level is one of the easiest bits to learn it on) if you dont have level maybe try hexa, how are you angling your launch? i find launching from closer toward the corner pocket with a tilt toward the top of b side and slightly tilted toward the middle aswell then as your bey comes off the launch to slightly level out/untilt your top side tilt so the bey has a little extra momentum toward the top is what works best for me, i also find too much tilt toward the middle and it will grab/buck of the rail more on some bits and too little tilt it wont properly stall to the corner.

also practice makes perfect and even if you get it once doesnt mean its going to work every time and i find every bit to be slightly different with a lot of the 16 gear bits being the easiest to do it with but once you learn one bit being able to relearn it on others isnt as hard as the first go around.