POST JSON

Hi,

I try to send a POST command to an API with this code :

var json = {
"machinecode": "E5",
"dispatchtypecode": "PANNE",
"description": "Temps de vide trop long > Chambre Droite",
"tradecode": "Maintenance"
};

var url1 = "https://xxx.com/api/1.0/dispatches/open/?auth=abcdefghij&site=50";

var params = {
headers: header /* JSON */,
url: url1 /* STRING */,
content: json /* JSON */
};

// result: JSON
var result = Resources["ContentLoaderFunctions"].PostJSON(params);

But I receive this return :

{"headers":"","success":false,"error":"Unexpected error in open. If problem persists contact Support."}

Could you help me, please ?