The <argument>
tags don't match exactly with your example command line, and a
is missing.
Perhaps it will work if you rewrite like this:
<argument>a</argument>
<argument>-tzip</argument>
<argument>-pMY_SECRET</argument>
<argument>-mem=AES256</argument>
<argument>secure.zip</argument>
<argument>/home/user/tmp/test.txt</argument>