VPN management system development requirements

1. The billing and management of such agreements as PPTP, L2TP, IKEV2, OPENVPN and SHADOWSOCKS should be supported. 2. Implement background management for users (for example, adding users, deleting users, freezing users, updating users, etc.) 3. To realize the package, including month, season, half year, one year, two years and three years. 4. Combining the monthly and the inclusive flow control and unlimited flow plan. 5. Free trial function. 6. Implement payment interface. 7. Realize one-time payment plan, such as 10 yuan 10G flow, unlimited time, and use up the package. 8. You can increase the VPN node without limit. 9. The payment will be made automatically after successful payment. 10. Provide API interface (including user registration, user login, Display the ping to each server, List all servers using the API aswell as download the config files from our servers and automatically check for new and updated ones and their country flag + server/city name) 11. Provide the node installation script for IKEV2 and SHADOWSOCKS protocol, and successfully connect with this server. 12. After the project is completed, provide all source code and installation instructions.