The challenge
Babbel, a leading language-learning platform serving learners worldwide, needed to move its entire recurring billing infrastructure from Adyen to Stripe. Billing is the kind of system where a mistake shows up on the P&L the same day. The migration required:
- Moving live recurring billing at serious scale without disrupting renewals
- Re-tokenizing card vaults and rebuilding PayPal and SEPA flows on Stripe rails
- Zero-downtime execution with complete auditability
- Coordination across engineering, product, finance, and data teams
- Fault-tolerant architecture for high-stakes billing operations
The approach
I was brought in as lead engineer and migration consultant to architect and execute the move.
Technical architecture
- Designed Stripe Billing flows — Setup Intents, payment method mandates, multi-method support across cards, PayPal, and SEPA
- Built test-covered, idempotent background jobs scheduled via AWS EventBridge
- Modular service objects and orchestrators with custom handling for retries, rate limits, and API anomalies
- Comprehensive verification and reconciliation pipelines with full reporting
Systems integration
- Integrated with internal systems via webhooks, Lambda triggers, and event buses
- Event-driven reconciliation on AWS (EventBridge, SQS, Lambda, ECS, CloudWatch) with automatic retries
- Consistent data flow and status propagation across decoupled systems
- Infrastructure deployed and monitored with Terraform at scale
Leadership
- Drove sprint planning and authored the technical specifications the migration ran on
- Owned edge-case strategy and rollout sequencing for billing risk
- Code reviews and verification oversight to guarantee migration integrity
- Acted as both lead implementer and strategic advisor to internal teams
The results
- Hundreds of millions in recurring revenue migrated to Stripe rails
- Zero downtime through the entire migration
- Customers kept their payment methods, auth, and billing cycles — nobody noticed
- Complete auditability and reconciliation of all payment data
- Fault-tolerant pipeline that absorbed API failures and edge cases gracefully
Stack
- Ruby on Rails
- Stripe Billing
- PayPal
- SEPA
- AWS EventBridge
- Terraform
- PostgreSQL