To use the Nuki Web platform, you have to activate Nuki Web with your Nuki smartphone app. Tap on the desired Smart Lock in the Nuki app and enter the lock settings. Then go to "Manage Smart Lock". Here you can find the option "Activate Nuki Web" where you can activate Nuki Web for your Smart Lock. Follow the instructions in the Nuki app.
If you want to manage multiple Smart Locks with Nuki Web, you have to activate each Smart Lock seperately for security reasons, so that it appears in your Nuki Web account.