The toy handcuffs are made keyless. No need to have a key, you can always open them.
There is left and right side for it. But can print one side two times, works also.
The pin should hold for some time, but can print from TPU like 98A, to make it last very long.

Holes might be tight, so harder push should click in place, but suggest to use super glue to make it hold.

I used standard paracord to tie them together, harder to fit through, but can do or use smaller diameter rope.

How to assemble, look at one of the pictures.
Printed in PLA, 0.24 layer height.