To enable online license validation, follow these steps:
1. Allow platform to login and specify platform password in your account. This password can match your account password or could be any other if you like.
2. Specify in ZModeler's Account Setup page your ZModeler account name and your platform password.

3. Press Ok and restart ZModeler.
4. Apply license key (if it's not applied yet). You should see a "Verification: checking online..." label while ZModeler checks validation online for your license key:

Then ZModeler will write usual "... Days left" and "Verification: passed today":

If you see a Verification : Failed in ZModeler, make sure your specified proper account and password. Also, it's a must to assign password in platform options and press "Submit" there. If you did it earlier, do it again, so password is properly ecrypted. If still no luck, disable online validation by removing account information on Account Setup page.
