Our system works inside Android, iOS, Windows, and any other mobile operating system. As long as you can send a proper key check to our API you can use our services.
That said, please check the app store TOS before implementing an external license system in your mobile app. Most app stores require you to use their payment systems and forbid attempts to circumvent their fees.
You will likely need to sell your app through their system alone, however there are a myriad of other reasons to use an external license key system if it is within the accepted use based on their TOS.
Please do your due diligence first.