    URL = "https://bin.openintegrations.dev";
    URL = URL + "/post";

    MIMEType = "text/markdown";

    Result = OPI_HTTPRequests.NewRequest()
        .Initialize(URL)
        .SetStringBody("# Hello world!!")
        .SetDataType(MIMEType) // <---
        .ProcessRequest("POST")
        .ReturnResponseAsJSONObject();