billing-automation

# Billing Automation Master automated billing systems including recurring billing, invoice generation, dunning management, proration, and tax calculation. ## When to Use This Skill - Implementing SaaS subscription billing - Automating invoice generation and delivery - Managing failed payment recovery (dunning) - Calculating prorated charges for plan changes - Handling sales tax, VAT, and GST - Processing usage-based billing - Managing billing cycles and renewals ## Core Concepts ### 1. Billing Cycles **Common Intervals:** - Monthly (most common for SaaS) - Annual (discounted long-term) - Quarterly - Weekly - Custom (usage-based, per-seat) ### 2. Subscription States ``` trial → active → past_due → canceled → paused → resumed ``` ### 3. Dunning Management Automated process to recover failed payments through: - Retry schedules - Customer notifications - Grace periods - Account restrictions ### 4. Proration Adjusting charges when: - Upgrading/downgrading mid-cycle - Adding/removing seats - Changing billing frequency ## Quick Start ```python from billing import BillingEngine, Subscription # Initialize billing engine billing = BillingEngine() # Create subscription subscription = billing.create_subscription( customer_id="cus_123", plan_id="plan_pro_monthly", billing_cycle_anchor=datetime.now(), trial_days=14 ) # Process billing cycle billing.process_billing_cycle(subscription.id) ``` ## Subscription Lifecycle Management ```python f...