It’s understandable that you’d think this breaks rule 5, but it does not. This is not a traditional plugin; it is serviceware, see rule 6: https://www.ads-software.com/plugins/about/guidelines/
“Serviceware” plugins are defined as plugins that merely act as an interface to some external third party service (eg. a video hosting site). Serviceware plugins ARE allowed in the repository, as long as the code in the plugin meets all other conditions. These are allowed even for pay services, as long as the service itself is doing something of substance. Creation of a “service” which does nothing but to provide keys or licenses or anything similar for the plugin, while the plugin does all the actual work, is prohibited. Moving arbitrary code into the service so that it can appear to do some work is also prohibited. This will be handled on a case by case basis and our judgment on any given case is final.
The only difference is that instead of requiring payment before you ever use it, I provide it completely unrestricted in features over a period you can comfortably use it and evaluate if it meets your needs.