Production-grade payment integration and webhook debugging for Stripe, Mollie, PayPal, SOFORT, and Klarna. I fix the issues that make payments fail silently: race conditions, missed IPN callbacks, double-charging, idempotency bugs, and webhook timeouts.
WHAT YOU GET
- Webhook debugging — full request/response tracing
- Race condition fixes (concurrent IPN handling)
- Idempotency layer implementation
- Retry logic with exponential backoff
- Failed transaction tracing and reconciliation
- Refund and chargeback workflow audit
- PCI DSS compliance review
- Detailed logging and monitoring setup
- Test environment with sandbox credentials
- Documentation of root cause and fix
PLATFORMS
- Stripe (Payment Intents, Subscriptions, Connect)
- Mollie (Payments API, Subscriptions, OAuth)
- PayPal (REST API, IPN, Webhooks)
- SOFORT / Klarna / Sepa Direct Debit
- WooCommerce, CS-Cart, custom Laravel checkouts
- Shopify payment apps
COMMON ISSUES I FIX
- Webhook fires but order never updates
- Customer charged but order shows as failed
- Duplicate orders from retry storms
- Subscription cancellation not propagating
- Refunds not reflecting in CRM
- Race conditions between IPN and frontend success page
MY BACKGROUND
15+ years full-stack development. Deep PHP and Laravel expertise (PHP 8.3, Laravel 12). Backed by TechnoPC GmbH (registered German IT company, HRB 114519) for professional VAT invoicing.
DELIVERY
Fixed-price preferred for scoped bugs. Typical turnaround: 1-5 days for diagnosis and fix. Free initial diagnostic review. EU/CET timezone with same-day response during business hours.
Languages: English (fluent), German (business), Turkish (native).