# Build your mobile app for iOS and Android

> App369 specializes in creating innovative, high-performance mobile applications that provide high-performance user experiences and drive business success.

Canonical: https://app369.com/service/mobile-apps/

Tell us what your app should do. App369 designs and builds it, then submits it to the App Store and Google Play from your own developer accounts. Based in Miami, Florida.

**Under the hood:** Flutter for one codebase on iPhone and Android, or Swift for iPhone-only apps, with Firebase or a Node.js backend on Google Cloud.

[**See my price **→](https://app369.com/instant-quote/?need=mobile) [**Tell us about your app**](https://app369.com/contact/)

## **Prefer a fixed price?**

Fixed scope, fixed price, paid upfront. The work happens in writing; no call needed.

- [**App Fix Ticket**from $450One reproducible bug in an existing mobile or web app, diagnosed and fixed.](https://app369.com/fixed-price/flutter-firebase-bug-fix/)
- [**AI-Built App Rescue**from $450A Lovable, Bolt or Cursor app checked end to end in 3 days, then its worst problems fixed at a fixed price.](https://app369.com/fixed-price/ai-app-rescue/)
- [**Firebase Security Rules Audit + Fix PR**$950Tests whether one user can read or edit another customer’s data, and fixes what it finds.](https://app369.com/fixed-price/firebase-security-rules-audit/)

Meet Simon

## How we build your app, in 60 seconds

Simon, App369's founder, on the written scope, the fixed price, test builds on your phone and the launch.

What we build

## **Full-stack mobile services**

01

### **Cross-Platform Flutter Development**

Build one codebase that runs on both iOS and Android.

02

### **User-Centric Design**

Our design process combines user research, interactive Figma prototypes, and usability testing to create interfaces that convert.

03

### **Scalable Cloud Architecture**

Our architecture supports real-time data sync, push notifications, and auto-scaling infrastructure.

04

### **Secure & Compliant**

Security aligned with OWASP Top 10 guidelines. We implement end-to-end encryption, biometric authentication, and HIPAA-compliant data handling where required.

How it works

## **Our process**

2. 01 ### **Discovery & Planning** We start by understanding your business goals, target audience, and app requirements to create a comprehensive development plan.
3. 02 ### **UI/UX Design** Simon designs intuitive, engaging interfaces that align with your brand and provide exceptional user experiences.
4. 03 ### **Development** Simon builds your app in Flutter, Swift or Kotlin, with automated tests and a build pipeline, and shares progress in writing.
5. 04 ### **Testing & QA** Rigorous testing across devices and platforms to ensure your app is bug-free, secure, and delivers a reliable experience.
6. 05 ### **Deployment** We handle the app store submission process and ensure your app meets all requirements for successful launch.
7. 06 ### **Maintenance & Support** Ongoing support, updates, and enhancements to keep your app running smoothly and evolving with your business needs.

Technologies

- Flutter
- Swift
- Kotlin
- Firebase
- Google Cloud
- TypeScript
- Vue
- Node.js

Error fixes

## App Store rejections we fix

Each page explains the rejection from Apple’s own guidelines, with what to change before you resubmit.

- [ITMS-90725 SDK version issue](https://app369.com/fix/itms-90725-sdk-version-ios-26/)
- [ITMS-91053 Missing API declaration](https://app369.com/fix/itms-91053-missing-api-declaration/)
- [ITMS-90683 Missing purpose string](https://app369.com/fix/itms-90683-missing-purpose-string/)
- [App Store Guideline 2.3](https://app369.com/fix/app-store-guideline-2-3-accurate-metadata/)
- [App Store Guideline 4.2](https://app369.com/fix/app-store-guideline-4-2-minimum-functionality/)
- [App Store Guideline 3.1.1](https://app369.com/fix/app-store-guideline-3-1-1-in-app-purchase/)
- [App Store Guideline 3.1.2](https://app369.com/fix/app-store-guideline-3-1-2-subscriptions/)
- [App Store Guideline 4.8](https://app369.com/fix/app-store-guideline-4-8-login-services/)
- [App Store Guideline 2.1](https://app369.com/fix/app-store-guideline-2-1-app-completeness/)
- [App Store Guideline 4.3](https://app369.com/fix/app-store-guideline-4-3-spam/)
- [App Store Guideline 5.1.1](https://app369.com/fix/app-store-guideline-5-1-1-data-collection/)

Error fixes

## Google Play problems we fix

Each page explains the problem from Google Play’s own help pages, with what to change next.

- [Google Play target API level](https://app369.com/fix/google-play-target-api-level-35/)
- [Google Play Billing Library version deprecated](https://app369.com/fix/google-play-billing-library-deprecated/)
- [App Bundle signed with the wrong key](https://app369.com/fix/google-play-app-bundle-wrong-key/)
- [Google Play Data safety form rejected](https://app369.com/fix/google-play-data-safety-form-rejected/)
- [Google Play Photo and Video Permissions](https://app369.com/fix/google-play-photo-video-permissions/)
- [Google Play foreground service declaration](https://app369.com/fix/google-play-foreground-service-declaration/)
- [Google Play version code already used](https://app369.com/fix/google-play-version-code-already-used/)
- [Google Play 12 testers](https://app369.com/fix/google-play-12-testers-14-days/)

Questions

## **Frequently asked questions**

### **How much does it cost to develop a mobile app?**

Cost depends on scope, platforms and integrations. Our rates are published on the fee structure page, and the free app cost calculator gives a range for a mobile app with every assumption listed. We send a fixed quote after reviewing your brief.

### **How long does it take to build a mobile app?**

Simple apps with core features take 2-3 months, medium-complexity apps with backend API integration and user management require 3-6 months, and complex enterprise applications with real-time features and CI/CD pipelines can take 6-12 months.

### **Should I build for iOS, Android, or both?**

Building for both platforms maximizes your addressable market.

### **What is Flutter and why do you use it?**

It compiles to native ARM machine code for both iOS and Android, delivering 60fps performance with a single Dart codebase.

### **Do you provide ongoing maintenance and support?**

Yes. App369 provides comprehensive post-launch support including bug fixes, OS compatibility updates for new iOS and Android releases, security patches, performance monitoring via Firebase Crashlytics, and feature enhancements. Our maintenance packages include CI/CD pipeline management and automated regression testing.

### **Can you help with app store submission?**

App369 handles the entire submission process for both Apple App Store and Google Play Store. Simon prepares all required assets, writes ASO-optimized descriptions, and ensures compliance with the latest Apple Human Interface Guidelines and Google Play Store policies. We also set up TestFlight for iOS beta distribution and Google Play's internal testing tracks.

## **Data and research**

- [**Mobile App Market Data 2026**](https://app369.com/statistics/mobile-app-market-data-2026/) App Store billings, iOS and Android share, smartphone ownership and app retention studies, each sourced.
- [**App Development Statistics 2026**](https://app369.com/statistics/app-development-statistics-2026/) App Store and Google Play economics, store fees and review times, mobile OS share and framework usage, each sourced.
- [**App369 Client Review Data 2026**](https://app369.com/statistics/app369-client-review-data-2026/) The public Fiverr reviews, counted: returning buyers, where they are and what they bought.

Start here

## **Launch your app in 3-6 months**

Whether you need an MVP or an enterprise platform, get a detailed estimate by email, usually within one business day, or book a consultation ($100 per 15 minutes, paid upfront).

[**Get in touch **→](https://app369.com/contact/) [**View pricing**](https://app369.com/fee-structure/)

Fiverr reviews / 95 on app work

## **What buyers said about this kind of work**

[**Read 126 of the 127 reviews **](https://app369.com/reviews/)

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### **Read the whole story**

- [Sixteen five-star reviews from one buyer: mobile apps, app design and a Shopify store](https://app369.com/case-studies/fiverr/mobile-apps-and-a-shopify-store-for-one-buyer/) (Mark, United States)
- [A large custom app build, delivered on the back end and the front end](https://app369.com/case-studies/fiverr/large-custom-app-build/) (A buyer in the United States)