Hey Gregor,
Thanks for using The Events Calendar!
I think you’ll find the information you need about how to use one license for multiple installations here. You should be able to apply the dev & live site set up to what you described here.
If you’re having trouble getting things to work as expected, I recommend reaching out to our support on the Events Calendar PRO premium forum. Over there, we have the capacity to provide more technical support. This Pre-Sales forum is reserved specifically for questions about the features of our plugins for users who are making decisions about which, if any, to purchase.
Let me know if I can clarify any of this!
Best,
Shelby 🙂