Custom VoIP System Development

Good day, everyone.

We are seeking a VoIP system developer to create the following features from scratch for our system:

We are VoIP resellers to call centers, BPOs, and marketing companies.
Currently, we have open-source VoIP billing software that can only perform billing tasks.

We are looking to provide a comprehensive solution to our clients:
1. A customer portal accessible from our website with a direct sign-up option.
2. The portal should allow customers to operate on a pay-as-you-go system, enabling them to recharge or pay their bills directly from the portal using various payment methods such as cards, bank transfers, or cryptocurrencies.
3. We aim to integrate a dialer system within our customer portal, allowing clients to create webphones for their agents/users and utilize other dialer or PBX features.

We are open to demonstrating our current working system to provide a better understanding of our requirements.
We are seeking a scalable solution, and if anyone has innovative ideas, we are more than willing to explore and collaborate on those as well.