Adding a Mobile App to a Marketplace That Already Works on the Web

If your marketplace already works on the web, the mobile app is mostly a new front end for what you have. Keep your backend and API as the single source of truth. Build the app on top of them, start with the side that does most of its work on a phone, and send the app to review early.

That’s how we built Traza’s app. Traza is an Australian marketplace for tattoo artists. Its team had a CTO, backend and web developers, a documented API and finished Figma designs, but no mobile developers, and no plan to hire any for at least six months. Our React Native team built the artist app on Traza’s live API for a budget under $20,000. It was approved on the App Store and Google Play and went live in early 2026 (Traza case study).

Do you need an app at all?

A responsive website works on phones. You need an app when one side of your marketplace does its job away from a desk and needs things a browser does badly:

• Push notifications that arrive right away: a new request, a message, a changed booking.
• Quick replies between other tasks, with one tap from a notification.
• The camera and photo library, for listings, portfolios or proof of work.
• A place on the home screen, so your marketplace is the first thing they open.

Traza’s artists are a clear example. Everything an artist did on Traza happened in a browser, which works at a desk. But tattoo artists spend the day on their feet, between clients, and they need to answer requests, plan sessions, take deposits and reply to messages from their phone.

If none of that applies to your users, a well-built mobile website may be enough for now.

Build the side that lives on the phone first

You don’t need two apps on day one. Pick the side whose daily work happens on a phone, and give them the app first.

For Traza, that was the artists. The first app covered the artist side of the marketplace from the first login to a finished session: 9 epics and about 22 user stories. Once that was live, a second phase for the client side (sign-up, login, messages, bookings and settings) was scoped and started, reusing the artist-side logic.

This order also matches common marketplace advice: serve the harder side first. Our guide to what a marketplace app costs covers supply, demand and which side to build for first.

Build on what you already have

The cheapest app is one that reuses your backend, your API and your designs instead of redoing them. Traza made that a rule from the start.

• Designs: Traza’s Figma files were finished, so there was no design phase. We treated Figma as the single source of truth and settled questions about a screen quickly. When the client’s director reworked a screen, that version became the new reference.
• API: the app talks to Traza’s live REST API.
• Messages and push: the app uses Traza’s own Firebase project.
• Ownership: Traza’s team owned the backend, and ours owned the mobile app.

Your API decides your speed

An app built on a live API can only move as fast as that API. At kickoff, a login error on Traza’s development API stopped our screen work until their team fixed it. After that, the two teams worked as one.

Before a mobile team starts, check that your API is ready for a phone:

• Login that works for an app: tokens that refresh, and sign-out on every device.
• Endpoints for push notifications and device registration.
• Paging on long lists, so the app doesn’t load everything at once.
• Photo and file uploads from a phone.
• A stable test environment the mobile team can rely on.
• A plan for old app versions. People don’t update right away, so the API must keep working for the previous release.

React Native or Flutter?

Both build an iPhone app and an Android app from one codebase, and both can handle a typical marketplace app. We’ve shipped both: Traza’s app is React Native, while Kosmo, LEV and HealthyNikah are Flutter. For a team adding an app to an existing web product, these differences matter most.

Question	React Native	Flutter
Language	JavaScript or TypeScript, with React	Dart
Fit with a React web team	Same language and ideas; web developers can read the code	A new language for the team
How the screens are drawn	Creates the phone’s own Android and iOS views	Draws its own interface, the same on every phone
Recommended start	The Expo framework, per React Native’s docs	The Flutter SDK
Stripe payments	Official Stripe React Native SDK	Community package (flutter_stripe), not reviewed by Stripe
Our apps	Traza	Kosmo, LEV, HealthyNikah

Sources: React Native docs and native components, Flutter architectural overview, Stripe SDKs, Stripe community SDKs.

Our rule of thumb: if your web team writes React and will look after the app later, pick React Native, because the people who know your product can work on both. If nobody on your team will touch the mobile code, and you want the app to look identical on every phone, Flutter is a strong choice.

Logins, accounts and payments

A few store rules catch web marketplaces off guard when they add an app.

Logins

Traza’s artists log in with Instagram or email, because Instagram is where artists already show their work. If your app uses a social login for the main account, read Apple’s guideline 4.8 first. It can require you to offer an equivalent login option with stronger privacy features next to it (Apple App Review Guidelines).

Account deletion

If people can create an account in the app, Apple requires a way to delete it inside the app (guideline 5.1.1(v)). Google Play also wants a web link for deletion requests (Google Play Console Help). If your web marketplace has no delete-account feature, your API needs one before launch.

Payments

Bookings for real-world services, like a tattoo session, are paid outside Apple’s in-app purchase system, with cards or Apple Pay (guideline 3.1.3(e)). So your existing payment provider keeps working. Traza’s artists take deposits from the app. We explain deposits, holds and no-show fees in how to create a booking app.

Plan the work in weeks, and cut early

Traza had three limits: a budget under $20,000, a launch date the client had already promised, and the rule to build on its API and designs. Here’s how the project held to all three:

• Weekly cycles on the client’s Jira, with regular demos. The client could change priorities every week.
• When the custom calendar grew bigger than planned, we cut it to a first version and moved push notifications and booking creation forward, because artists needed those more.
• To protect the launch date, we added a second developer early.
• When one developer dropped out mid-project, we covered the cost and gave the work to the other developer, so the budget and timeline stayed the same.
• Mid-project, the client added two more epics, and they still fit inside the budget.

App Store review is the last risk. Traza’s case notes that review can take one to two weeks, which is risky with a fixed date. Apple says it reviews 90% of submissions within 48 hours (Apple App Review), but rejections add rounds. So we sent the app to review early instead of polishing it until the last day. It was approved on both stores.

What it costs, and who builds it

Traza’s artist app had a team of four: a senior React Native developer, a React Native developer, a delivery manager and a QA engineer. The budget was under $20,000.

Option	Best when	Cost with us
Fixed-scope first app	You know what the first app must do	MVP from $5,000 to $15,000, 2-4 weeks
Mobile developers added to your team	You have a CTO and want mobile people working inside your process, like Traza	$6,000-9,000 per developer per month, start in 2-4 weeks
Weekly sprints after launch	The app is live and you’re adding features	About $3,000-4,500 a week

Traza is the second option in practice: two mobile developers added to an in-house team that kept the backend. Our dedicated team page explains how that model works.

On top of the build, budget $99 a year for Apple’s developer program and a one-time $25 for Google Play.

A checklist before you start

1. Decide which side gets the app first, and why.
2. Make sure your API has mobile login, push endpoints, paging and uploads, and a stable test environment.
3. Finish the designs, or agree that the app copies your web flows at first.
4. Choose React Native or Flutter based on who will maintain the app.
5. Add account deletion to your API if you don’t have it.
6. Agree who owns what: your team the backend, the mobile team the app.
7. Plan to send the first build to review early.

If you want a team that has done this, see our marketplace app development page. If your marketplace doesn’t exist yet, start with our guide on launching a niche marketplace.

FAQ

Should I build a mobile app or a mobile website for my marketplace?

Build an app when one side needs instant push notifications, quick replies, the camera, or works away from a desk. Traza’s artists needed all of that between clients. If your users mostly browse and book now and then, a well-built mobile website may be enough at first.

Can a mobile app use my existing web API?

Yes, and it should. Traza’s app runs on Traza’s live REST API and its Firebase project. Check first that the API supports mobile login with refreshing tokens, push notifications, paging and photo uploads, and keep a stable test environment for the mobile team.

Should a marketplace app use React Native or Flutter?

Both work. React Native suits teams that already write React, and Stripe ships an official SDK for it. Flutter draws its own interface and looks the same on every phone, and Stripe support comes from a community package. Traza’s app is React Native; our Flutter apps include Kosmo and LEV.

Which side of the marketplace should get the app first?

The side that does its daily work on a phone and is harder to keep. For Traza, that was tattoo artists, who answer requests and take deposits between clients. The client app came in a second phase and reused the artist-side logic.

How much does it cost to add a mobile app to a web marketplace?

A fixed-scope first app costs $5,000 to $15,000 with us and takes 2 to 4 weeks. Traza’s artist app, built on its own API and designs, came in under $20,000. Mobile developers added to your team cost $6,000 to $9,000 per developer per month.

How long does App Store review take for a marketplace app?

Apple says it reviews 90% of submissions within 48 hours, but a rejection and resubmission add more time. On Traza we allowed for one to two weeks, so we sent the app to review early. It was approved on the App Store and Google Play.

See what your app would cost

Tell us what your marketplace does on the web and who needs the app. Our AI estimate turns it into a scope, a budget range and a timeline in about four minutes.

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