Hi Hermann,
Thanks for reaching out, and I’m so sorry for the trouble here! You’ll see the Event Aggregator license key field appear as soon as you’ve installed the free version of The Events Calendar–that’s because the functionality of Event Aggregator is built into the core of The Events Calendar, and it’s unlocked via license key with no need to install anything else. However, Events Calendar PRO is a separate download that’s installed alongside The Events Calendar, so you’ll need to install both plugins to get the license key field for Events Calendar PRO. You can find instructions on how to download and install our free and premium plugins on our Knowledgebase article here. Once you’ve done that, our new user primer will walk you through the remaining steps to get set up! 🙂
I hope that helps to get you all squared away here! Thanks again, and let us know if you should have any other questions!