You tested out your passcode key, and it worked great. But now it stopped asking for a passcode.
One of these two things (or both!) is probably happening:
Locksmith is remembering your browser.
When you enter your passcode, Locksmith remembers it for the browser session. Try closing out the browser and reopening. Locksmith should prompt for the passcode again.
Locksmith is remembering your account.
If you were signed into a customer account when you entered the passcode, Locksmith will remember that passcode on that account, and never ask again when you're signed in.
This happens by default on the passcode key, but you can change this setting:
Head into the lock and edit the key by clicking on the pencil icon on the key. Next, click advanced settings and disable the option "Remember for signed in customer".
Then click Update Key. :)