Turn a key (key plate) after inserting it gently and at right angles into the keyhole.
Applying too much force may cause the lock to malfunction.

Amount of force used to operate an indirect-action lock
Never use a force in excess of 20 cN∙m to turn the key (key plate).
If a greater force than this is needed to turn the key, there is a possibility that the handle is not in thte correct position for locking.
Check the angle of the handle or the stroke, and return the handle to the correct position for locking.
An indirect-action lock product consists of the lock being incorporated in the handle or other part with locking done by the handle’s stopper plate or latch mechanism. Its structure prevents further movement of the stopper plate or latch.
Examples: A-140, A-240, A-377, FA-602, FA-815, etc.

Amount of force to operate an indirect-action lock