Hi Kamailio users,
I'm trying to setup Kamailio as a Diameter Routing Agent, but I just can't seem to get the diameter_request() function to actually send a diameter request, I just get a warning about no JSON Response:
WARNING: ims_diameter_server [avp_helper.c:341]: addAVPsfromJSON(): No JSON Response

Inside my event route I've got one line to send the data to the peer "ims-hss.localdomain":
event_route[diameter:request]{
      diameter_request("ims-hss.localdomain", $diameter_application, $diameter_command, $diameter_request);
      xlog("Forwarded Diameter Request");
}

Hard as I try I can't seem to get this request forwarded to this peer and see that next xlog() line.
In the config file I've included the cdp_check_peer & cdp_has_app checks to confirm the peer is up, and able to accept the request, (full config in pastebin below)
I've defined the peers in the diametercfg.xml config file, and they're all showing as online when I do a "kamcmd cdp.list_peers":
                FQDN: ims-hss.localdomain
                Details: {
                        State: I_Open
                        Disabled: False
                        Last used: 0
                        Applications: {
                                appid:vendorid: 16777216:10415
                                appid:vendorid: 16777216:4491
                                appid:vendorid: 16777216:13019
                                appid:vendorid: 16777216:0
                                appid:vendorid: 16777217:10415
                                appid:vendorid: 16777221:10415
                        }
                }

The source of avp_helper.c shows the warning is called if the length of the JSON is <= 0, but as I'm feeding back out what I've received it's not 0, an no recent major changes to the source, so I'm stumped as to why it's catching this.

I'm running Kamailio 5.1.2 on Ubuntu 18.04 installed from Repos.
Full Kamailio Config: https://pastebin.com/afgqUfWr
Diameter CDP Config XML: https://pastebin.com/bVrBG8mG
Relevant Syslog: https://pastebin.com/ZY8z2kd4
Kamcmd cdp.list_peers: https://pastebin.com/cKi4JAHC

Any ideas as to what am I missing?

Thanks in advance!

Nick