Modena

Challenge

Modena sells bathroom and interior decoration products with average prices between 800 and 8000 RON per order, a category where installment payment is a critical factor in purchase decision. They needed integration with BT iPay3 for cards (with 3DS support and pre-authorization for in-stock products with delayed delivery) and TBI Bank integration for interest-free installments over 12-24 months. Plus an architecture that could simultaneously process installment payments through TBI and card payments through BT, without confusing user sessions. The existing code was monolithic custom PHP with years of evolution; any radical change risked destabilization.

Solution

We implemented both payment integrations directly on the existing codebase, with strict separation between payment logic and product logic, to avoid interfering with existing functionalities. For BT iPay3 we built a two-phase flow (authorization at checkout, capture at delivery confirmation) to avoid holding funds for out-of-stock products. For TBI Bank we implemented RSA encryption for requests, server-side validation of interest calculations (TBI calculates independently, we verify reconciliation), and a webhook handler that marks the order as paid only after TBI confirmation. All critical requests are logged with unique identifier for audit. User sessions don't mix between payment types, a user who chooses TBI installments cannot complete with card on the same session, avoiding race condition bugs. Recoverable restart was tested on 50 real sessions before production launch.

Process

1. 01Discovery with Modena team on real order flows and product categories
2. 02BT iPay3 and TBI Bank API documentation, edge cases identification
3. 03Sandbox environment with BT test cards and TBI test environment
4. 04Progressive implementation with feature flags per payment method
5. 05Audit logging for each transaction with client/order correlation
6. 06Gradual launch: 10% test traffic, monitoring, expansion to 100%
7. 07Tested and documented rollback procedure for each integration