From the CLI tool

add user passwd=bla
*Debug(7)* parse_input: add user passwd=bla
["passwd=bla"]
{:command=>:adduser, :parameters=>{"passwd"=>"bla"}}
*Debug(10)* json_obj: json_obj: authe29c821d61cc1fa597359c4df0df9ce3id2methoduser.addparamspasswdblajsonrpc2.0
*Debug(8)* do_request: Sending: {"auth":"e29c821d61cc1fa597359c4df0df9ce3","id":2,"method":"user.add","params":[

],"jsonrpc":"2.0"}
*Debug(8)* do_request: Response Code: 200
*Debug(8)* do_request: Response Body: {"jsonrpc":"2.0","error":

,"id":2}
An error was received from the Zabbix server
Error code: -32500
Error message: Application error.
Error data: Incorrect parameters pasted to method [ user.add ]

The error message returned is overly simplistic. In this case something to the effect of what fields are required would be useful.

Also as an aside, pasted? Perhaps "Incorrect parameter for method [user.add", just a thought.