Hello,
With the error message you are seeing my guess would be that you might possibly have an older version of humann2 installed. We added the uniref90 ec filtered database in humann2 v0.7. However, you mention you have v0.9 installed so I would think you should be okay to download the database.
Can you run the following command? It will list the databases available for download based on the humann2 version you have installed. If you do not see the database in the list, is it possible you have more than one humann2 version installed on your system and this command is running the older version? If you do see the database listed, can you try running the download command again after double checking your command format (ie sometimes the format from a copy/paste to the terminal can pick up some unexpected formatting).
$ humann2_databases --available
Thanks!
Lauren