Complete subscription management system for Joomla extension developers. Generate and manage download keys with tiered subscriptions (trial, standard, premium, enterprise). RSA-2048 signature-based key verification with domain binding. REST API for remote licence validation. Dynamic update server with environment-specific download URLs. Built-in extension directory with access model controls (free, trial, paid). Usage tracking, analytics, and automated expiry notifications. New Upsell signals queue — clearer and better scoped.