Hi and welcome to Just Answer. My name is XXXXX XXXXX have been repairing Computers and Electronic Devices Professionally for over 13+ years and currently own a Shop in FL.
Press the Top down as your unlocking it with the key. This should allow for the latch to move. If the key turns but the Top doesnt open then the spring loaded mechanism has become loose in the back of the lock. You'll then need to press the top down and shake the safe while holding it at a right angle and the key in the unlock position to try and get it to slide off. You may need to take a butter knife and gently pry it as your attempting to unlock it.
If the Mechanism is so bad off that it wont open after the above options and you must get to the internals, you'll have to pry it open causing the mech to bend. It wont be easy as this one is waterproof and very tight.
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