Integrate Slack, Calls, and Stripe

I need a skilled developer to integrate a messaging, calling, and payment system into my website using Flask, Python, and PostgreSQL.

Key Integrations:
- Messaging: Slack
- Calls: Both voice and video
- Payment: Stripe

Ideal Skills and Experience:
- Proficient in Flask and Python
- Experience with PostgreSQL
- Familiarity with Slack API
- Experience integrating Stripe for payments
- Background in implementing voice and video call functionalities

Please ensure the system is secure and scalable.