After another year of usage it's necessary to pay the maintenance fee for WL.
When I click on "Purchase now" in the Authentication Wizard, it brings me to the Website to purchase the full Version.
Where can I purchase the maintenance only?
greetings
Erich

Got it :-)
... it's in the wizard, but two steps later....

Activating Wealth-Lab Developer

QUOTE:
Renewing maintenance period

Customers can renew their maintenance period by clicking on the "Renew maintenance" link label inside the Authentication Wizard. This will redirect you to our payment gate. Please keep in mind that all operations concerning accepting payment orders and prolonging maintenance period are manual, and your payment order will be processed as soon as possible within 1 business day. When your order is processed, you can authenticate Wealth-Lab Developer with the same license key you've been using (a key never changes).