Rezerve

Online booking for Turkish local businesses — salons, barbers, clinics. An owner sets up services and hours, and gets a public page where customers book, and can pay a deposit (kapora), without an account. The UI is in Turkish.

Live: rezerve-iota.vercel.app

• Book as a customer at /r/demo. Cilt Bakımı takes a ₺300 kapora through iyzico's sandbox: use a test card such as 5311 5700 0000 0005 with any future expiry and any CVC.
• Run the business at /giris as [email protected] / rezerve-demo (Pro), or [email protected] / rezerve-demo (free plan: the same services, but the kapora is not collected).
• Both demos reset every morning, so change anything.

Worth a look

• Fifty simultaneous bookings for one slot, and exactly one wins. A Postgres EXCLUDE USING gist constraint over the time range decides, pending holds included, and the race is a test. Run with the constraint dropped, eight of the fifty got the slot: the app's own availability check catches most of a race, never all of it.
• Times are right in the business's own timezone, DST included. Bookings are stored as UTC instants, opening hours as wall-clock minutes in whatever timezone the business picks. Turkey has had no DST since 2016, so the slot engine is tested on New York's spring-forward and fall-back days instead. Closer to home, iyzico stamps Istanbul wall-clock times with a Z; the payouts page does not take them for UTC, which would show every payment three hours late.
• iyzico, probed rather than assumed. A marketplace account has no Abonelik — every /v2/subscription/* call returns 100001, and iyzico's integration team confirmed it — so Rezerve runs its own renewals, from a card taken in its own form: a PCI trade-off made knowingly, in the sandbox. The payouts page was corrected once for counting money iyzico still held as the owner's, and when iyzico's daily transaction listing stopped listing on 23 September, it moved to asking about each booking by its own id.

Stack

Next.js 16 (App Router, Cache Components) · React 19 · TypeScript · Tailwind v4 + shadcn/ui (Base UI) · Postgres (Neon) + Drizzle ORM · Better Auth · iyzico · React Email + Nodemailer · Bun · Biome · Vitest · Playwright

Engineering notes

Card handling, deliberately

Upgrading to Pro takes the card number in Rezerve's own form (/panel/abonelik), and a server action passes it to iyzico's direct payment API with registerCard: 1, without 3-D Secure. The number is never logged and never stored; only the returned cardToken and cardUserKey are kept, for renewals.

On an iyzico marketplace account that is the only way recurring billing works: the hosted Checkout Form carries no card object, the hosted card vault (/v2/ucs/init) answers 42205, and iyzico's integration team points recurring payments at card storage on the direct API. (Why this is a marketplace account at all is under Why there is no iyzico Abonelik integration.)

Against the sandbox, with test cards, that costs nothing. With real cards it would cost two things this build deliberately stops short of. A card number passing through the server puts the whole deployment in PCI DSS scope — SAQ D, not the SAQ A a hosted payment page allows. And the first payment would have to go through threedsInitialize for 3-D Secure; renewals stay non-3DS either way, since the customer is not there to authenticate.

Why there is no iyzico Abonelik integration

iyzico does not offer Abonelik on a marketplace account. Their integration team was explicit: "Pazaryeri iş modelimizde tekrarlı ödemeler abonelik özelliği ile sağlanamamaktadır" — recurring payments in the marketplace business model are done with card storage instead. The API agrees: every /v2/subscription/* endpoint returns 100001, before and after the account was switched to marketplace.

The two products are account modes, not independent flags — the enablement email says the account's iş modeli was "updated to" marketplace. And the SDK shows why they can't coexist: no subscription request model accepts a submerchant field, so iyzico's subscription engine has no way to route a recurring charge to a submerchant. On a marketplace account, it is switched off wholesale.

So Rezerve owns its own billing schedule:

This is the beginning of the README. Read the rest at the original. Read the full README ↗