Custom WhatsApp Business API Integration

I'm looking for a professional to integrate the WhatsApp Business API for my business. The integration needs to support multiple key functionalities, including sending and receiving messages, handling client calls, and assigning conversations to various agents.

Key Project Requirements:
- **Communication Management**: The API should facilitate both sending and receiving messages, as well as managing client calls.
- **Multi-Agent Support**: Conversations need to be assignable to multiple agents, ensuring efficient customer service.
- **Cross-Platform Functionality**: The solution should be accessible and functional on both web and mobile platforms.
- **Custom User Interface**: A bespoke UI for managing conversations and agent assignments is essential. This UI should be intuitive, user-friendly, and able to handle the demand of high-volume interactions.

Ideal candidates for this project should have:
- Extensive experience with the WhatsApp Business API
- Proven track record in developing custom UIs
- Strong skills in cross-platform application development
- Excellent understanding of multi-agent system design
- Highly proficient in managing real-time communication systems.

If you can deliver a seamless, robust, and efficient solution, I look forward to your proposal.