I'm writing a plugin, I want to put in a WordPress repository, but I need a simple and PRO license. I wanted to do obfuscation of php code, but it is forbidden by WordPress rules. How can I do that?
You can use a strategy referred to as "freemium" where you distribute a free version of your technology but require users to pay for an enhanced version (often with more features and support).
To implement the paid license is a topic more complicated and diverse than can be answered in-depth here. But the short & sweet of it is you have a separate website with users, of which each paid copy of your technology is a member of and must login to in order to update.
You can have your plugin in the WP repository. Or you can have obfuscated code.
But not both.
Some have a partial-feature plugin in the repository, and then a full-featured non-repository plugin that is downloaded from your web site. But you have to have an update-checking process in the paid/non-repository version.
There's no point having a license checker in a plugin in the WordPress repository. You can't require it for updates, because updates are delivered by the repository, and you can't require it to unlock features, because you're not allowed to do that in the repository either, for licensing reasons.
If you distribute a plugin via the WordPress repository it needs to be free and open source. That's the rules.
You can charge for your plugin, and require a license for updates and support, if you distribute the plugin yourself or via another platform. In that case the way you'd implement license checking depends entirely on the platform you're using to sell license keys. You will need to check their documentation.