Hi,
I`am trying to use this module and got the same issue.
I made a quick look into code. The problem lied in ims_diameter_server.c in function diameter_request wich start at line 263 In this function in line 311 made call to function addAVPsfromJSON with empty parameter s_message To resolve this, we need fill s_message with data by calling get_str_fparam
I made a quick patch. [kamailio_ims_diameter_server.txt](https://github.com/kamailio/kamailio/files/5895410/kamailio_ims_diameter_ser...)