Android App Development: Road Tax Seva

I'm seeking a professional Android developer to build a custom app named Road Tax Seva with the following features:

- Secure Login/Signup via Phone Number and OTP
- GST Invoice Generation
- Payment Gateway Integration (already available)
- RTO Data Sync API Integration

The app must be clean, fast, and easy to use.

Preferred Skills & Experience:
- Proven experience in Android app development
- Strong background in secure authentication methods
- Familiarity with GST and RTO data
- Experience with payment gateway integration
- Based in India (preferably Gurgaon)

Please share:
- Past work samples
- Estimated cost
- Timeline

Looking forward to your bids!