Custom Payment Gateway Integrations & Fintech Solutions
Implement secure checkouts, bank APIs, recurring subscription billings, and reliable transaction mapping for your platforms.
In any web-based business, processing payments securely and reliably is the absolute key to cash flow and customer trust. A poorly integrated checkout system can lead to abandoned carts, double-charge issues, failed subscription renewals, and data exposure vulnerabilities. Standard 'out-of-the-box' plugins often fail to support complex billing logic, custom multi-tier payment splits, dynamic cashback programs, or localized banking gateways. Crafting high-performance payment engines requires an engineer who understands financial security and concurrency.
I am Maksudur Rahman, a dedicated Backend Engineer specializing in custom payment gateway integrations and fintech development. Having spent years building and optimizing transaction services tailored for the Turkish fintech ecosystem (such as Sipay), I understand the intricacies of bank integration. I specialize in designing double-entry ledger database architectures, implementing distributed locks to prevent double-billing under heavy load, and structuring normalized adapter layers to standardize inconsistent banking payloads.
My payment integration services are built for security, high-performance, and flexibility. Whether you need to integrate global processors like Stripe and PayPal, set up local bank APIs, build multi-vendor split-payment contracts, or establish secure webhook processors that reconcile transaction states, I build payment architectures that execute without error.
Key Specializations
Global Gateway Integrations
Integrating credit card processors and digital wallets including Stripe, PayPal, Braintree, and Adyen. I implement secure card vaulting, custom checkouts, and multi-currency billing structures.
Local Bank API & Direct Bank Integrations
Connecting systems directly to local banking networks for low-fee processing. I specialize in writing custom PHP/Laravel integration adapters for specialized national fintech networks.
Subscription Billing & Recurring Payments
Architecting automated subscription models. I construct recurring billing plans, grace-period rules, automated invoice mailings, and secure dunning processes to handle failed credit card payments gracefully.
Double-Entry Ledger & Audit Logging
Designing secure, mathematically balanced database ledgers. I implement atomic database entries and immutable transaction history logs to prevent balancing errors.
Atomic Webhook Processors & Reconciliations
Building bulletproof webhook handlers to capture asynchronous payment notifications. I prevent data corruption by validating signatures and checking transaction history before updating states.
Custom Split-Payment Contracts
Designing logic to divide checkout payments between platform owners and vendors. I build automated commission calculations, escrow systems, and payout sequencing.
Proven Track Record
My work at Softrobotics Bangladesh Ltd was heavily focused on designing, building, and optimizing advanced payment gateway solutions for the Turkish fintech ecosystem. I have integrated multiple local banks and payment aggregators, building custom middleware to manage high-throughput callback data.
- Sipay Fintech Integrations: Designed and developed payment routing endpoints, customized transaction check steps, and handled API interactions with major local Turkish banks.
- Provider Error Mapping: Implemented normalized error translation layers, translating cryptic, inconsistent bank responses into user-friendly notifications, increasing successful transaction rates.
- Distributed Redis Lock System: Implemented distributed locks on payment callback endpoints, blocking duplicate concurrent webhooks from creating double-payment anomalies.
- Kodersolution Split Payments: Programmed dynamic billing logic allocating automated split payments between contract software developers and agency platform owners via Stripe.
My Development Process
Billing Analysis & Design
We analyze your billing structures, compliance needs (PCI-DSS), local payment preferences, and transaction flows. I model the database schema to handle transaction states securely.
Gateway & Adapter Setup
I write normalized API adapters to interface with the payment gateway. I establish secure API handshake methods and create data structures to store transaction payloads.
Checkout Flow & Webhooks Integration
I build the checkout user flow, implement card authorization, and integrate webhook callbacks. I ensure webhook endpoints validate signatures to prevent fake request injections.
Concurrency & Lock Testing
I simulate heavy concurrent users and network drops to verify that lock mechanisms prevent double-processing and that background queues retry failed callbacks.
PCI Auditing & Deployment
I verify that no sensitive card details (CVV, PAN) are stored in the database. Once audited, I deploy the checkout system to production with continuous transaction logging.
Technical Stack
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