export ltm monitor https password

You dont have to export the master key. You just have to set the master key same in both the boxes to get this working. When you load an encrypted config into another box, it validates the passphrase configuration against the master key.

Follow these steps:

Login to your primary LTM where you have the monitor config.

tmsh show sys crypto master-key
tmsh modify sys crypto master-key prompt-for-password
enter password: mynewpassword
password again: mynewpassword
tmsh show sys crypto master-key

You would notice the old hash and the new hash of your new password when you run show sys crypto command.

Login to your second LTM where you want the monitor to be loaded.

tmsh show sys crypto master-key
tmsh modify sys crypto master-key prompt-for-password
enter password: mynewpassword
password again: mynewpassword
tmsh show sys crypto master-key

Now that both the boxes have the same master-key, the config can be copied and loaded in the second ltm.

tmsh load sys config merge from-terminal

This should work. Thats how we handle the singletons or l7 boxes (standalone L7 LTM's)