CRM Email Automation & VoIP Integration

I'm developing a project with Flutter frontend and Firestore backend. I need help implementing three key functionalities:

Email Sending & Automation: Using Postmark. Need setup for at least welcome and follow-up emails.

Phone/SMS VoIP Integration: Using Telnyx. Integrate into my CRM for direct client communication.

APIs: Help with any other necessary API functionalities.

Currently using Replit for webhooks but will migrate to Railway after development.

Looking for a developer with experience in:
- Flutter
- Firebase/Firestore
- Postmark and Telnyx APIs
- Webhook integrations

Need this done ASAP!