FreePBX-Dinstar SIP Registration Fix

My Dinstar GSM gateway needs to register cleanly to FreePBX so that any call hitting the SIM in the gateway is forwarded to a MicroSIP client already registered on the same LAN. At the moment the gateway refuses to register, and every sign points to a network-level configuration problem rather than authentication or timeout issues. All three devices—FreePBX, the Dinstar gateway and MicroSIP—sit on the same subnet, so I would like a fresh set of eyes to trace, correct and document whatever is blocking the SIP handshake.

Here is what I need from you:
• Join me through AnyDesk or TeamViewer for live troubleshooting and configuration.
• Adjust FreePBX trunk settings, Dinstar SIP parameters and any required NAT / firewall rules until the gateway registers and call flow works end-to-end (SIM ➜ Dinstar ➜ FreePBX ➜ MicroSIP).
• Prove success with a test inbound call and, if possible, an outbound call from MicroSIP via the GSM channel.
• Provide a concise step-by-step document of every change you make so I can replicate or reverse it later.

Tools in play include FreePBX (latest stable), Dinstar gateway web GUI / CLI, MicroSIP, and basic network utilities such as ping, traceroute and packet capture should they be needed.

Acceptance criteria:
1. Dinstar gateway shows “Registered” status in both its own interface and FreePBX.
2. Incoming GSM call rings and is answered on the MicroSIP client with two-way audio.
3. Delivered documentation clearly lists settings altered on FreePBX, Dinstar and the network.

If you have solid SIP troubleshooting skills and are comfortable working live over remote desktop, this should be a straightforward engagement.