@Straticah Unless you're already comfortable with the AWS ecosystem it might be overkill for something this simple.
You could check out Trigger.dev or other lightweight serverless function apps.
Or you could roll your own license validation using an automation platform like Make (https://make.com) very easily.
All you really need is a way to make a POST request with the license key, which will return an "active/inactive" response. You should also compare the email associated with the license with the email supplied by the user.
EDIT: looks like you might even be able to do all this within HISE using the Server.callWithPOST()
function.
https://docs.hise.dev/scripting/scripting-api/server/index.html#callwithpost