Recurring Revenue Infrastructure Is the Agency Retainer Moat

Agencies that own the subscription and billing layer stop selling hours and start governing a client's cash flow, which converts project work into multi-year retainers. The strategic risk is lock-in: the platform that automates invoicing, tax, and dunning also becomes the system a client cannot leave without a migration project. Choosing the billing stack is therefore a client-retention decision, not a procurement decision.