Hi B 4liano,
Well… technically it’s one license per install, but there’s a bit of a workaround that could apply here. You could purchase just one license but install the plugin on all of your domains. You can associate the license with only one of those installs, but that gets you access to support and the updates of the plugin. On the one site with the license, those updates can be done through the autoupdate process. However, for the remaining installs you would have to download the plugin and update them manually.
So, no but yes. Is that clear for you?
— Julie