Just to be clear this is ONLY for V15 and there is going to be a fix in the Template shortly, but for now:
1) Download the attached zip file and, take the XML file and copy it into folder C:\ProgramData\3CX\Instance1\Data\Http\Templates\gateway\ on the 3CX Server, overwriting the existing one.
2) Restart all 3CX Services and nginx service.
3) Configure the Gateway in V15. For reference use the V14 guide, the logic for the most part is the same:
http://www.3cx.com/voip-gateways/patton-smartnode-sn4112/
4) Once the Gateway is registered, in the V15 Management Console go into SIP Trunks, highlight the Gateway Settings, press Edit and then go to the "DIDs" tab.
5) Here the logic is the same as in 'Step 7' in the aforementioned V14 guide with one key difference.
Instead of creating DIDs 0, 1, 2, 3 that correspond to the 4 physical ports of the GW, create
0000, 0001, 0002, 0003.
6) Once you have created 0000, 0001, 0002, 0003, in order to configure the routing of each one of them, follow the guide here:
http://www.3cx.com/docs/manual/inbound-rules/
This is just temporary, we are planning on both releasing the fixed template online and updating our configuration guides in the near future.