This drove me nuts for 2 days.
Velcro, 2-sided tape, GoPro strap, jerky, bouncy, humming, vibration, etc.
Finally got it (at least for my gimbal)
There is a mounting channel on top of the camera with a little locking spring in there:
Got a few 6-32 x 3/4" machine screws (to fit in the channel)...