Basic server-side Kamailio SIP proxy with NAT traversal for 3CX PBX

I have a 3CX server hosted on Azure with a public IP address. However, the client IP phones are behind NAT and common NAT traversal techniques such as STUN and TURN are cannot be used. I am configuring an outbound SIP proxy server using Kamailio. There is no database or authentication required. The Kamailio server should perform the following functions: 1. Perform NAT traversal on any incoming or outgoing SIP connections using the "nathelper" module 2. Simply relay the SIP connection to an EXISTING PBX server (3CX). ***Kamailio should relay ALL SIP requests to 3CX. This is a very basic setup, and Kamailio should not be performing any authentication, register, or other PBX functions.*** I installed Kamailio on CentOS 7.4, and I have written a configuration script to perform this these functions, but it is not working as intended. I have been able to get it to NAT REGISTER requests but some requests (INVITE) from the 3CX PBX are not being NAT'd. The end working result should be that an IP phone behind NAT will be configured for the Kamailio outbound proxy in the phone settings. This phone should be able to register with 3CX, as well as make and receive calls. No configuration should be required on the client-side - everything should be server-side (similar to any cloud IP PBX service). You must have prior experience with Kamailio/SER, SIP, as well as a firm understanding of networking and NAT. I can provide remote access to the server through Teamviewer or other requested methods. If you already have a working Kamailio route config script that does this as intended, I can also just pay you for the configuration script as long as it works. Please let me know if you have any questions, I will be happy to provide more information.