Hermeticdental – Jamali dev

Overview

A billing engine the team could actually trust

The client was running their subscription billing on a tangle of spreadsheets and a third-party tool that didn't fit their multi-tenant model. They needed a platform of their own — one that could issue thousands of invoices a day, never double-charge a customer, and be hardened enough to hold sensitive financial data.

I designed and built it solo on Laravel 11: a clean, tested codebase with role-based access, a queue-driven PDF pipeline, and a Stripe integration that reconciles itself. No starter kit shortcuts, no plugin soup — every layer was written to be understood and maintained.

The challenge

What was breaking

The old setup couldn't keep up — and every edge case cost the team real money and trust.

Concurrent requests occasionally double-charged customers
PDF generation blocked the request and timed out at scale
No tenant isolation — a real risk for financial data

How I solved it

Each problem mapped to a deliberate, testable architectural decision.

Race-safe reservations via DB transactions & row locks
PDFs moved to a queued job with Redis & retry logic
Tenant scoping enforced globally at the model layer

Code highlight

Race-safe charging, by design

The core fix: wrap the charge in a database transaction with a row lock so two concurrent requests can never bill the same invoice twice. Simple, boring, and bulletproof.

app/Services/ChargeService.php

public function charge( Invoice $invoice ): Payment
{
    return DB::transaction( function () use ( $invoice ) {
        // Lock the row so concurrent requests wait their turn
        $invoice = Invoice::lockForUpdate()->find( $invoice->id );

        if ( $invoice->isPaid() ) {
            throw new AlreadyPaidException();
        }

        $payment = $this->gateway->capture( $invoice );
        $invoice->markPaid( $payment );

        return $payment;
    } );
}

What I built

Key features

Subscription engine

Plans, proration, trials, and dunning — reconciled automatically against Stripe webhooks.

Queue-driven PDFs

Invoices render in a background job with retries, so the UI never blocks or times out.

Role-based access

Granular permissions and tenant isolation enforced at the model layer, not the view.

Hardened & audited

2FA, signed webhooks, encrypted secrets, and a full security header set out of the box.

“

Our Laravel dashboard handles thousands of bookings a day without a hitch. The architecture is clean and the handover docs were genuinely excellent.

DK

David K.

CTO, Logistics SaaS