Is there a special trick to remove a set of Bren Brno cuffs ; like a certain way to manage the key's movement?

I wasn't able to remove them for over an hour!
Almost went to the Fire Department.
But I definitely didn't want to have to have them cut off!
Thanks for everyone's support and friendly advice.
Sincerely,
TL 

If the shackle is fastened tightly, then to open the lock, you need to press the movable shackle a little to reduce the pressure on the lock tooth