Cross-Platform Real-Time Mobile App Development

I'm seeking an experienced mobile app developer to create a real-time mobile application with comprehensive functionalities. The app needs to be developed for both iOS and Android platforms.
Key requirements:
- Implement secure Email/Password authentication system
- Integrate PayPal as the sole payment gateway
- Incorporate an SMS gateway for communication purposes

Ideal candidates should have:
- Proven track record in cross-platform mobile app development
- Expertise in integrating payment and SMS gateways
- Strong understanding of secure user authentication systems
- Experience with real-time application development

Please share your previous work samples that align with these requirements.