SEND: {"auth":"3fb846473a3fb10f755f1a550e1814c2","method":"usergroup.update","id":1,"params":{"userids":[

{"userid":"100100000000007"}

],"usrgrpids":{"usrgrpid":"100100000000012"}},"jsonrpc":"2.0"}

RECV: {"jsonrpc":"2.0","error":

{"code":-32500,"message":"Application error.","data":"Internal zabbix error"}

,"id":1}

I've also tried different variations of the params array, since it isn't clear what the correct layout should be, but they all gave the same uninformative error message..