Mysql AES_DECRYPT problem. Not being able to decrypt the password

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Project Budget (USD)
$10 - $30

Project Description:
A freelancer developed for me a wordpress plugin that let users input some data, and the data is then ecrypted using AES and then saved on my database.

He used phpseclib.

The plugin he made is able to decrypt the passwords for me, but the thing is, I need to be able to decrypt them using MySQL queries.
I'm using mysql 5.6.

When I execute queries like this:
SELECT AES_DECRYPT(FROM_BASE64(`password`), MD5('encryption)_key')) FROM sometable;

It returns a null value.

I need you to look on the source code and figure out what's going on, or provide me a way to decrypt the passwords using mysql queries.

Skills required:
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