How do authors commonly handle this situation:
I have a plugin for Wordpress that I’d like to start selling here but want to make sure to limit it to 1 domain. So the user will need to unlock the plugin after installing with their purchase code but they shouldn’t be able to do that on multiple domains.
You can add optional features like auto updates, demo content downloads and so on which require buyers to submit their purchase code.
However (it’s a very discussed and quite grey area) rendering the plugin entirely unusable from installation without purchase code submission would probably not be allowed.