AES_ENCRYPT and AES_DECRYPT

Im trying to encrypt a password to be held in a database, however I need to know the password to authenticate against another system so need to be able to decrpyt it again.

So to encrypt the password Im using:-

INSERT INTO `suppliers`.`users` (`username`, `password`) VALUES ('user1', AES_ENCRYPT('mypassword','cryptstring'))

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And then to decypt it Im using:-

SELECT `username`,  unhex(AES_DECRYPT(`users`.`password`,'cryptstring')) FROM `suppliers`.`users`

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Which should work, however it returns as a decrpted password as '6d7970617373776f7264' which I initally thought was HEX representation of the password but when I try to run it through unhex it just returns null

Any ideas?