Are online and offline activations possible for the same license?

Yes, our Activation Server solution provides both online and offline activation.
https://www.sciensoft.com/products/eleckey/activation-server
The app connects via web services to the Activation Server to request for license activation. Here is a sample of web services provided by the server:
https://demo.eleckey.net/service.asmx
In case of offline, you can do it manually by logging on the server control panel:

https://demo.eleckey.net/activationmanager.aspx

Username: Administrator

Password: Administrator

Or, you can set up a web-based activation like the following sample page:
https://demo.eleckey.net/registration_activation.aspx