ftp mdtm: invalid command

Greetings.

Thank you for the excellent inetutils.

I'm using the FTP utility, which supposedly supports the MDTM command (as
per section 21.1 Standards of the documentation):
https://www.gnu.org/software/inetutils/manual/inetutils.html

However, when I try mdtm, it complains: "invalid command".

For testing purposes, I've used the quote command:

    quote "mdtm myfilename.ext"

which returns a timestamp correctly.

ftp> mdtm 20230518T213000Z.gps.new
?Invalid command
ftp> quote "mdtm 20230518T213000Z.gps.new"
213 20230521012942


So, the server recognizes the command correctly.

Am I missing something?

Thank you!
-Felipe.