You can use the same license key on two separate domains, e.g. for your development and production websites. Furthermore, subdomains and domain names that contain the words "dev", "staging" and "test" are not taken into account when considering the two-domain limit. This is because the update server's license validation system has been designed to ignore these types of domain names.
If you have more than two domains, you can use the same license key on all of them for a transitional period of up to 48 hours. During this time, you can switch the domains associated with the license key as often as needed (for example, when moving from a staging site to a production domain).
There is no need to re-activate or deactivate the domain because the old domain will automatically disappear from logs. The update server request logs are carefully inspected and analyzed in order to identify any potential abuse. Should any be found, your license key may be restricted, which will prevent you from using the automatic update feature of the plugin from within your WordPress admin dashboard.
If you have a WordPress website that uses a multisite configuration and has multiple domain names, it is still considered one environment. This is true, for example, when you use separate domain addresses for each language version. Therefore, if you have such a website, you just need to buy the "single domain" variant, and the "multi domain" license is not required.