Payment processing
One-off charges and checkout flows integrated with Stripe, PayPal, Braintree or Square, with cards tokenized so raw data never hits your servers.
App Backend & API · Payments & Billing · AI-First · Results-Driven
Payments & BillingSubscriptions and Charges Wired Into Your Backend
Short answer: Payments and billing is the backend work that lets your app take money: one-off charges, recurring subscriptions, invoicing, and usage-based billing, integrated securely with a processor like Stripe, PayPal or Braintree. Done well, cards are charged reliably, subscriptions renew and cancel correctly, and webhooks keep your database in sync with the payment provider; done poorly, customers are double-charged, failed renewals go unnoticed, and revenue quietly leaks. Zen in Tech builds payment integrations in-house using PCI-compliant patterns and tokenization, so raw card data never touches your servers. Judge the work on correct handling of edge cases, webhook reliability, and accurate reconciliation between what was charged and what your records show.
Getting paid, without surprises
Payments and billing is where your app turns usage into revenue, and it is unforgiving: a bug here does not just annoy a user, it charges the wrong amount, misses a renewal, or blocks a paying customer. The backend job is to integrate a payment processor, record every transaction accurately, keep subscriptions in the right state, and produce invoices and receipts, all while never storing sensitive card data yourself.
The hard part is not taking a single payment, it is the edge cases. Cards expire and get declined; customers upgrade, downgrade, pause and cancel mid-cycle; refunds, proration and taxes have to be exact. This is handled through webhooks, the events a processor like Stripe sends when a payment succeeds, fails or a subscription changes, made reliable with idempotency keys and signature verification so a repeated event never double-charges. Card details are tokenized so they go straight to the processor, keeping you within PCI-compliant patterns. Watch for missed webhooks that leave your database out of sync, and reconciliation gaps where your records and the processor's disagree.
Because we build billing as part of your backend, the payment state always matches your app's own data: an active subscription means real access, a failed payment triggers the right follow-up. We wire in webhooks, retries, invoicing and clear reconciliation from the start, and we lean on trusted platforms like Stripe rather than touching raw card numbers, so security and accuracy are built in, not bolted on.
What we cover
What our payments & billing work covers
Subscriptions & recurring billing
Plans, trials, upgrades, downgrades, proration and cancellation handled correctly through the full subscription lifecycle.
Invoicing & receipts
Automatic invoices, receipts and billing history your customers and accounting team can rely on.
Webhooks & payment events
Reliable webhook handling with signature verification and idempotency keys, so your database always matches the processor.
Usage-based & metered billing
Track usage and bill per unit, seat or tier, so customers pay for exactly what they consume.
Secure, PCI-compliant handling
Tokenization and PCI-compliant integration patterns so you take payments without ever storing sensitive card data yourself.
Services
Payments & billing services we deliver
From a first checkout to complex metered subscriptions, here is how we wire payments into your backend, correctly.
Payment gateway integration
Integrate Stripe, PayPal, Braintree or Square for secure one-off and recurring charges, with cards tokenized end to end.
Subscription & billing system build
A complete subscription backend: plans, trials, proration, dunning for failed payments, and cancellation, all in sync with your app.
Add payments to an existing app
Retrofit checkout, subscriptions or invoicing onto a product that currently has no way to take money.
Migrate billing providers
Move from one processor or billing tool to another, carrying customers, subscriptions and payment methods across cleanly.
Usage-based / metered billing
Build metering and rating so you can charge per API call, seat, or unit of usage accurately.
Reconciliation & billing reporting
Wire up reporting that matches your records to the processor's, so revenue, refunds and failed payments are always accounted for.
Tools & platforms
The payments stack we build on
The exact toolset depends on your goals — these are the platforms we use most, and we work with whatever your team already relies on.
Subscriptions & billing
Stripe BillingChargebeeRecurly
Tax & compliance
Stripe TaxAvalaraPCI DSS SAQ-A patterns
Reliability
idempotency keyssigned & verified webhooksretries
Data & records
Chosen per project — not a fixed menu. Have a preferred tool or platform? We’ll work with it.
Built to last
Secure, Accessible & Built to Last
We build on modern, well-supported frameworks with security and accessibility baked in — dependency hygiene, input validation, HTTPS and WCAG-minded UI — so your product is safe and usable from day one.
You own all the code and assets. Everything ships with documentation and a clean handover, so your team (or ours) can maintain and extend it without lock-in.
Who we work with
Industries We Build For
20+ years across sectors — in Houston and internationally.
Transparent pricing
Estimate your project in seconds
Pick what you’re building for an indicative range, then request an exact quote. No email wall.
Simple prices for typical tasks
- App APIfrom $10k
- Backend + authfrom $18k
- Realtime / scalefrom $25k
- Care planfrom $1k/mo
Proof
700+ projects, 20+ years
See the products and growth work we’ve shipped across industries — and request a case study relevant to yours.
How we work
Fixed scope. Sprints. Working software.
- 01
Scope & fixed estimate
A short discovery call turns your idea into a clear spec and a firm range — free.
- 02
Design & architecture
UX, data model and stack chosen for your scale, not ours.
- 03
Build in sprints
Working software every 1–2 weeks — you see progress, not promises.
- 04
Launch & scale
We ship, measure and keep improving with care plans.
FAQ
Payments & billing: frequently asked questions
How much does payment and billing integration cost?
It depends on scope. A straightforward Stripe checkout is often a few thousand dollars, while a full subscription system with trials, proration, dunning and metered billing costs more. Payment work is usually scoped inside a backend build, which typically starts around $10,000. Processor fees (such as Stripe's per-transaction rate) are separate and paid to the provider. We confirm the exact figure on a free call.
What does payments and billing development actually involve?
It is the backend work of integrating a payment processor, recording every transaction, keeping subscriptions in the correct state, handling invoices and taxes, and syncing all of it with your app through webhooks. The goal is that charges, renewals, refunds and access are always accurate, and that sensitive card data never touches your own servers.
How long does it take to build payments?
A single checkout or payment flow typically takes one to two weeks. A full subscription and billing system with proration, dunning and reporting takes longer because of the many edge cases. Migrating an existing billing setup depends on data volume. We give a firm timeline once we know your pricing model and requirements.
Is it PCI compliant, and do you store card numbers?
We build to PCI-compliant patterns and do not store raw card numbers on your servers. Card details are tokenized by the processor (such as Stripe), so sensitive data goes straight to them and your backend only ever handles a token. This keeps you in the lightest PCI compliance tier and dramatically reduces your risk. Note that we build the integration; we cannot enter your financial credentials for you.
Do you build payment systems for businesses outside Houston?
Yes. We are based in Houston but build payments and billing for clients across Texas, the USA, and internationally. The work is delivered remotely, and processors like Stripe support multiple currencies and regions, which we configure to match where your customers are.
Do you help Houston businesses take payments in their apps?
Absolutely, it is our home market. Our office is at 9800 Richmond Ave in the Westchase / Energy Corridor area, and we can meet in person to plan checkout, subscriptions or invoicing for your product. Everything is built in-house by our own specialists.
Which payment processor should you use?
For most apps we recommend Stripe for its strong developer tools, subscription features and documentation, but PayPal, Braintree and Square all fit certain businesses better depending on your customers and existing accounts. We are processor-agnostic and recommend the fit for your model and region on a free call, rather than defaulting to one.
Wire payments in without the surprises
Reliable charges, subscriptions that stay in sync, and secure, PCI-compliant handling. We'll scope your billing backend on a free call. Get a fast estimate from our Houston team.
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