If you are using a bobby pin, be sure to remove the plastic tip if there is one.
The bent tip of your makeshift key should only fit halfway into the handcuff lock.
Remove the key to feel it. The end of your key should now be in a sort of “Z” shape.
If you are successful, the handcuffs should click open.
The tightness should create a tension in the tie that makes it easier to break.
The locking mechanism is essentially a small notch that digs between the tracks of the zip tie as you tighten it, keeping it secured.