The fact that the parameter name is plural and it accepts an array of objects may trick someone into believing that a proxy can have multiple interfaces. The parameter should be called "interface" and it should accept a single interface object. Keep in mind, that the "interfaces" parameter must still be supported for backward compatibility.

Proxy create must look like:
{
"host": "bbb",
"status": 6,
"hosts": {},
"interface":

{ "hostid": 10164, "ip": "127.0.0.10", "dns": "localhost", "useip": 1, "port": "10051" }

}

Proxy update must look like:
{
"host": "aaa",
"status": 6,
"hosts": {},
"interface":

{ "interfaceid": 56, "hostid": 10164, "ip": "127.0.0.10", "dns": "localhost", "useip": 1, "port": "10051" }

,
"proxyid": 10164
}