Openhab REST API and UNITY

Dear all,
With Javascript I can control item from my website.
With Unity I can’t.
I try a lot of script like GitHub - proyecto26/RestClient: 🦄 Simple HTTP and REST client for Unity based on Promises, also supports Callbacks! 🎮
But it doesn’t work. For the moment I always have the problem : 415 Unsupported Media Type, but I can not put text/plain in the headers, I don’t know how to do this.
Any idea?

OMG, after few hours, it was just a bad custom of my request :

currentRequest =

        new RequestHelper {

            Headers =

                new Dictionary<string, string> {

                    { "Authorization", "Basic " + encodedText }


            Uri = basePath + "/switchNeosmart",

            BodyString = "ON",

            ContentType = "text/plain", //HERE

            ParseResponseBody = false,

            EnableDebug = false